E. A. Smith

“ Frequently the individuals of a colony are grouped into systems, in which the atrial orifices open into a common cloaca. The little ascidiozooids vary greatly in shape in the different families. In the Polyclinidæ, for instance, they are long, the organs being so to speak, drawn out, and being arranged in three regions, the thoracic, abdominal and post-abdominal, the first region containing the branchial sac, the second the stomach, and the third the heart and reproductive organs. ”

“ The breathing-organs. Thread-like processes on either side of the body, the so-called gill-filaments, often unite with those in front of and behind them, and so give rise to plates; these, when well developed, are best seen in the division to which the Oyster and the Mussel belong, and which, therefore, has been called the division of the plate-gilled Molluscs, or Lamellibranchia. Where the body is coiled or twisted on itself, as so often happens, the gills of one side may be altogether lost. ”

“ The “Worm-shells” (Vermetidæ) are a very peculiar family. Their shells can scarcely be distinguished from the shelly tubes which are formed by certain species of marine worms, Serpula, &c. They are free and spiral in early life, but afterwards become distorted and generally attached to rocks, stones, &c. A foot for walking purposes therefore would be of no use; consequently it is more or less obsolete, serving only as a support to the operculum.
Case 48. The “Screw-shells” (Turritellidæ) have elongate tapering shells; about 100 recent and 200 fossil species are known. ”

“ Water enters at the mouth, and, by the contraction of the muscle-hoops, is driven out through the atrial aperture at the opposite end, which is then closed by a sphincter muscle. The elastic walls of the body expand, and water again enters through the mouth, the valve-like lips of which prevent its being driven out that way. The Salpa swims along in jerks, and along with each gulp of water takes in Radiolaria, Foraminifera, etc., which are retained by the mucus of the endostyle and carried to the gullet. ”

“ The two valves are always in contact at the hinge, which is generally formed by small interlocking projections or hinge-teeth, and they are closed by large adductor muscles, which are attached to impressions in the interior of the shell. When these muscles cease to act, as after death, the valves of the shell open in consequence of the elasticity of the ligament on the dorsal margin. The majority of species have two principal adductors, one at each end, like the Venus-shells, Cockles, Razor-shells, &c.; but in Oysters, Scallops, and a few others, there is but a single central muscle. ”

“ The Acmæidæ are called False Limpets, because, although the shells are identical with the true Limpets, the animals differ in having only a small gill on the left side of the neck, whilst the Patellæ have the gills greatly developed all round the sides of the foot. Both the true and the false Limpets are littoral and found on rocks between tide-marks. They have the power of excavating the surface to which they attach themselves, and adhere so firmly that it is easier to break the shell than detach the animal. ”

“ The Pholadidæ, or Piddocks, are very remarkable shells, of an unusually complicated structure, some having the power of boring into rocks, wood, mud, sand, etc. Their shells are white, adorned with prickly sculpture, and, although thin, are strong. The foot is believed to be the principal excavating instrument, but the shell no doubt is used as a file to enlarge the hole as the creature grows. These animals are brightly phosphorescent; and certain species are eaten at many places on the shores of the Mediterranean. They appear to be indifferent as regards the material they bore into ”

“ The species of Octopus are found on the shores of almost all temperate and tropical seas; they do not attain to a large size, and are without the internal shell or “bone” which is found in the mantle of many Cephalopods. That of the Cuttlefish or Sepia (Fig. 43 a) is found in abundance on our coasts; it is composed of numberless layers of a friable calcareous substance. That of the Squid tribe is of quite another character, consisting of an elongate thin horny plate, and strengthened by one or more thickened ribs, in some species somewhat resembling a quill-pen. ”

“ Many of the species are beautiful objects on account of the brilliancy of their colouration, and some are remarkable for the variation they exhibit in this respect. Species of Helicidæ are found in nearly every part of the world and in all situations, from sea-level to an altitude of 12,000 feet. They are fond of moisture, and in hot and dry weather retire within their shells, remaining torpid until the return of dew and rain. ”

“ Owing to their small size and transparency, it is possible to examine specimens alive under the microscope, the currents passing through the stigmata in the walls of the branchial sac, and the beating of the heart being distinctly visible. The rapid motion of the cilia surrounding stigmata gives the appearance of dark wheels all rotating in the same direction. The heart beats so as to drive the blood current so many times in one direction, and then after a short pause, in the reverse direction. ”

“ In tropical countries some assume a state of torpidity (æstivate) during the hottest and driest season of the year, closing up the aperture of their shells with a temporary lid or door (epiphragm) , in order to resist the dryness of the atmosphere. Some of these “summer-sleepers” are endowed with a remarkable tenacity of life. An Australian Pond-Mussel has been known to live a year after being removed from the water; several Land-Snails have revived after a captivity of from two to five years, without any food whatever. ”

“ They are unprovided with shells except in the earliest stages of their existence, when they dwell in a minute nautiloid shell, furnished with an operculum, both of which are subsequently cast off. Unfortunately the colours of these beautiful creatures cannot be preserved after death, and therefore a small series of glass models is exhibited, which will give some idea of their great variety in form and colouring. They are found in most parts of the world, chiefly in shallow water, but a few species live upon floating seaweed in the open sea. ”

“ Echinoderms are of great geological age, and were very abundant in earlier periods of the world’s history. Two groups (the Blastoids and Cystids) have completely disappeared, and the Stalked Crinoids (Lily-Encrinites) are far less common than they used to be. Echinoderms are now found in all seas, and extend to great depths of ocean; many of the species have exceedingly wide areas of distribution, and most are characterized by their gregarious habits, a large number of specimens of a single species being generally obtained by the dredge. They are most abundant in the tropical seas. ”

“ The Myidæ, popularly known as “Gapers,” on account of their valves being open at one or both ends, have the mantle united all round, except where the small foot is protruded. The siphons are very long, united almost to the ends, and covered with a coarse wrinkled outer skin. They bury themselves in mud and sand at low-water mark or in shallow water. The species are few in number, and chiefly from the shores of northern countries. Mya arenaria of our own coasts is largely eaten in some parts of Europe and North America. ”

“ Bivalves do not creep about in search of food, but find their means of existence in the shape of minute particles, both animal and vegetable, which happen to be contained in the water which they breathe. ”

“ Like the Limpets they hold on to the rocks with such tenacity that it is absolutely impossible to remove some of the larger species by force without injuring the shell. Boiling water or mustard and water poured over them will, however, soon compel them to relinquish their hold. The shell of Haliotis is pierced by a series of holes parallel with the left margin. Through such of them as are open the animal protrudes a slender filament or feeler, and the water also finds its way through them to the gills beneath. ”

“ In addition to the sexual, there is an asexual reproduction by means of peculiar internal buds termed statoblasts (Fig. 21) . When the colony dies in the autumn, the liberated buds, securely protected in a horny capsule, retain their vitality till the spring; in due season the valves of the statoblast burst open, and the contents develope into a new colony. The statoblasts, which resemble small seeds, are usually provided with a ring of air cells, which act as a float, and in some species spines are present.
71 ”

“ The small foot, which is brown in the common species, is not much used in creeping about, but has the power of spinning a byssus or bundle of tough threads, by means of which the animals attach themselves to rocks and one another, forming colonies of vast numbers. Mussels have always been much eaten in this and other maritime countries, and large quantities are brought to the London market from the Dutch coast. ”

“ The animals do not glide like most other molluscs, but scramble along like the Strombs, the form of their foot being small, divided into a front, expanded, and a hind, tapering portion admirably adapted to the nature of the ground on which they live, which usually consists of broken and dead shells.
Cases 49–52. The “Wing-shells” (Strombidæ) are the largest of the Gastropods with a proboscis or non-retractile snout. They do not crawl like most other Gastropods, but progress by a sort of hopping movement. They act as scavengers, feeding on decomposing animal matter. ”

“ Presently the tail becomes absorbed, and the posterior end of the nerve-tube, and the brain with its eye and hearing organ, undergo atrophy, the nerve ganglion of the adult alone representing the cerebrospinal axis of the larva. The branchial sac and intestines develop greatly, and growth proceeds in such a manner that the mouth is pushed round to a position opposite to the fixed area, and gradually the animal becomes the adult ascidian. ”

“ The hole or slit gives passage to a tubular fold of the mantle, through which the water apparently flows to the gills. The largest species are from California and South America, and others are found, but not abundantly, on most shores. The animal of the large Lucupina crenulata from California is eight or ten inches in length, and almost conceals the shell, and the shell of the South-African Pupillæa aperta is also all but hidden beneath the mantle of the animal.
Fig. 5. [3]
Pleurotomaria adansoniana. ”

“ Like the Snails, they are fond of damp localities, and at times become great pests to farmers in devouring the young shoots of the growing corn. Testacella, which is found in this country, differs from the Slugs in having an external shell at the tail-end of the foot. It is not slimy, and lives under ground, feeding upon earthworms. ”

“ They have no foot; the mantle is entirely open, with double edges, each being bordered by a short fringe, and the labial palps are large and somewhat triangular. There are on each side a pair of simple gills, which appear closely striated; the single adductor muscle is large and nearly central (see Fig. 30) . The Oyster is, except in the very young state, entirely incapable of locomotion, and always attached by the deeper valve to other shells, rocks, or other substances. The common British species is not full-grown until it is about five or seven years old. ”

“ A model of the anterior end of the common Tapeworm shows the four suckers and the crown of hooks; the unjointed neck is followed by the joints (proglottids) , which increase in size the farther they are from the neck. Several entire specimens of Tænia follow, showing the size of the whole worm and the form of its joints. The structure of the body is shown in the models of two joints. The growth and development of the Tapeworm is dependent on a migration or a change of the hosts which it inhabits in the various stages of its life ”

“ The branchial and atrial orifices are at the opposite 104ends. The branchial sac is pierced by two oblique bands of stigmata (Fig. 23 sg) . The life history is very complicated. The egg develops into a tailed larva, which develops into a “nurse”; the latter is asexual, and produces three kinds of buds on a stolon, viz. (1) nutritive buds which provide the “nurse” with food, (2) foster forms which are set free as cask-shaped bodies with eight broad muscle-bands, and (3) sexual forms which are attached for a time to the foster forms, but which later become free and give rise to the egg. ”

“ The next family, Veneridæ, have long respiratory siphons and a sinuated pallial line. Many of this tribe are very beautiful in form and colouring, and most of them have very hard strong shells. The valves are united above by an external ligament, and the hinge-plate is toothed. Nearly all of them live buried an inch or two beneath the sand or mud, but a few are found burrowing in rocks. Probably the majority of the species of this family might be used as food. ”

“ The Limas (Limidæ) are very like the Pectens, but the inner edge of their mantle is fringed with very long thread-like filaments. The shells are always white, generally more or less oblique, and radiately ridged. They appear to be found in most seas, and either swim about freely like the young Scallops by flapping their valves 38or attach themselves by a byssus, sometimes forming a sort of nest, consisting of pieces of coral and shell or small stones, in which they are completely concealed. ”

“ Cases 6 & 7 contain specimens illustrating the curious habit of self-mutilation possessed by so many Echinoderms; among Starfishes, and notably in the genus Linckia, the single arms separated from the disk are able to develop a fresh disk and arms, and so to multiply the species. Cases 9–11 contain fine series of Oreaster.
Ophiuroidea, or “Brittle-stars.”—These Echinoderms appear to resemble the ordinary Starfish [25] ; but they differ in having the organs of digestion, respiration, and reproduction confined to the disk, the arms having merely the function of locomotor organs. ”

“ The Loxosomidæ do not form colonies, owing to the buds becoming detached from the parent. The species of Loxosoma are always found associated with some other animal, such as a worm or Tunicate. The tentacles of the polypide are arranged obliquely to the long axis of the body, hence the name of the family (loxos, oblique) . Loxosoma phascolosomatum (*) occurs, in the form of delicate tufts, on the caudal end of the Sipunculid worm Phascolosoma. The individuals resemble pins with little white heads, and are capable of vigorous movements to and fro ”