Arthur Everett Shipley

“ There is further a great tendency for the endothelial cells to form muscles, and this is especially pronounced in the small arm-sinus, where a conspicuous muscle is built up. The mantle-sinuses which form the chief spaces in the mantle are diverticula of the main coelomic cavity. In Discinisca they are provided with a muscular valve placed at their point of origin. They contain the same fluid as the general coelom. The stalk is an extension of the ventral body-wall, and contains a portion of the coelom which, in Discinisca and Lingula, remains in communication with the general body cavity. ”

“ The Desmoscolecida move by looping their bodies like geometrid caterpillars or leeches, as well as by creeping on their setae. The mouth is terminal, and leads into a muscular oesophagus which opens into a straight intestine terminating in an anus, which is said to be dorsal in position. The sexes are distinct. ”

“ The reproductive cells are modified coelomic cells, which lie on the ventral vessel. They escape into the coelomic fluid and there develop. When mature they leave the body through the nephridia. Bonellia and Hamingia are very interesting examples of sexual dimorphism. The female has the normal Echiuroid structure, but the male is reduced to a minute, flattened, planarian-like organism, which passes its life usually in the company of two or three others in a special recess of the nephridia of the female. ”

“ The ovary and testes are heaped-up masses of red or yellow cells due to a proliferation of the cells lining the coelom. There are four of such masses, two dorsal and two ventral, and as a rule they extend between the outer and inner layer of the mantle lining the shells. The ova and the spermatozoa dehisce into the body cavity and pass to the exterior through the nephridia. ”

“ The Priapuloidea are dioecious, and their male and female organs, which are one with the excretory organs, consist of a pair of branching tufts, each of which opens to the exterior on one side of the anus. ”

“ The insect, which may have become an imago with the Gordian larva still in it, is then eaten by a carnivorous insect or by a fish, and the contained Gordian larva becomes elongate and mature in its second host. After a year or more this larva emerges into the water and commences to reproduce.
The unexpected occurrence of these worms in pools and puddles, often in great numbers, has given rise to myths about showers of worms. They occasionally make their way into the human stomach with the drinking-water and are vomited; but this is a case of pseudo-parasitism—they are no true parasite of man. ”

“ The valves are distinguished as dorsal and ventral. The ventral valve is usually the larger, and in many genera, such as Terebratula and Rhynchonella, has a prominent beak or umbo, with a circular or otherwise shaped foramen at or near its extremity, partly bounded by one or two plates, termed a deltidium. Through the foramen passes a peduncle, by which the animal is in many species attached to submarine objects during at least a portion of its existence. ”

“ There is a well-developed brain dorsal to the mouth; this gives off a pair of oesophageal commissures, which surround the oesophagus and unite in a median ventral nerve-cord which runs between the longitudinal muscles to the posterior end of the body. From time to time it gives off minute circular nerves, which run round the body in the skin and break up into a very fine nerve plexus. There are no distinct ganglia, but ganglion cells are uniformly distributed along the ventral side of the cord. ”

“ The whole is anteriorly somewhat loosely slung to the skin, so as to allow free play when the animal is extending or retracting its introvert. A pit or depression, known as “the cerebral organ,” opens into the brain just above the mouth; this usually divides into two limbs, which are deeply pigmented and have been called eyes.
Sipunculoids are dioecious, and the ova and spermatozoa are formed from the modified cells lining the body-cavity, which are heaped up into a low ridge running along the line of origin of the retractor muscles. ”

“ They are cylindrical worm-like animals, with a median anterior mouth quite devoid of any armature or tentacles. The body is ringed, and often has circles of spines, which are continued into the slightly protrusible pharynx. ”

“ Fertilization takes place outside the body, and in some species the early stages of development take place in a brood-pouch which is essentially a more or less deep depression of the body-wall median in Thecidea, while in Cistella (? Argiope) there is one such pouch on each side, just below the base of the arms, and into these the nephridia open. ”

“ The last named is oval and formed of four rows of large cells; it is separated by a sphincter from the rectum, which opens posteriorly and dorsally. The nitrogenous excretory apparatus consists of a coiled tube on each side of the stomach; internally the tubes end in large flame-cells, and externally by small pores which lie on the edges of the ventral row of scales. A cerebral ganglion rests on the oesophagus and supplies the cephalic cilia and hairs; it is continued some way back as two dorsal nerve trunks. The sense organs are the hairs and bristles and in some species eyes. ”

“ In some less primitive genera, e.g. Terebratula, that type of opening is found in the young stages only; later it becomes partly closed by two plates which grow out from the sides of the delthyrium. These plates are secreted by the ventral lobe of the mantle, and were named by von Buch in 1834 the “deltidium.” The form of the deltidium varies in different genera. The two plates may meet in the middle line, and leave only a small oval opening near the centre for the pedicle, as in Rhynchonella ”

“ Scattered hairs cover the body. Just in front of the anus there is in Chaetosoma a double, and in Tristicochaeta a triple row of about fifteen stout cylindrical projections upon which the animals creep. The females are a little larger than the males; in Ch. claparedii the former attain a length of 1.5 mm., the latter of 1.12 mm. The mouth opens into an oesophagus which passes into an intestine; this opens by a ventral anus situated a little in front of the posterior end. The testis is single, and its duct opens with the anus, and is provided with a couple of spicules. ”

“ Unfortunately almost every anatomist who has written on the muscles of the Brachiopoda has proposed different names for each muscle, and the confusion thence arising is much to be regretted. In the Testicardines, of which the genus Terebratula may be taken as an example, five or six pairs of muscles are stated by A. Hancock, Gratiolet and others to be connected with the opening and closing of the valves, or with their attachment to or movements upon the peduncle. ”

“ The ventral vessel, which ends solidly behind, sends off a branch which forms a ring around the intestine and opens into the posterior extremity of the dorsal vessel. In Echiurus and Thalassema the same vessel forms a ring round a stout muscle, which connects the bases of the two ventral setae before passing to surround the intestine. Amoeboid corpuscles float in the fluid contents. The nephridia vary in number from a single one in Bonellia to three pairs in many species of Thalassema. ”

“ The anterior segment broadens and becomes umbrella-shaped; it has a powerful row of cilia round the rim and smaller cilia on the general surface. By the aid of these cilia the larva swims actively, but owing to its minute size it covers very little distance, and this probably accounts for the fact that where brachiopods occur there are, as a rule, a good many in one spot. The head bears four eye-spots, and it is continually testing the ground (fig. 29, A, C) . The second segment grows downwards like a skirt surrounding the third segment, which is destined to form the stalk. ”

“ At its attachment to the body the groove sinks into the mouth. In Bonellia the proboscis is forked at its free end, but in the other genera it is short and unforked. The body is somewhat sausage-shaped, with the anus at the posterior extremity, surrounded in Echiurus by a single or double ring of setae. The skin is usually wrinkled, and in B. viridis, Thalassema lankesteri, Th. baronii, Hamingia arctica, and in the larva of many species, is of a lively green colour. ”

“ The Nematomorpha are nearly solid,—quite so at each end, and only in the middle region of the body are there any body-cavities, the space within the body being usually filled up with parenchyma. There are four closed spaces of the nature of body-cavities, two lateral and a dorso-median and a ventromedian. Into the former the ovaries project, though the lumen of the lateral body-cavity is quite shut off from the lumina of the ovaries or uteri. In the adult male the lateral body-cavities are absent. ”

“ Like the chief arm-nerve, this strand runs through the lophophore, parallel indeed with the former except near the middle line, where it passes ventrally to the oesophagus. The lophophore is supplied by yet a third nerve, the under arm-nerve, which is less clearly defined than the others, and resembles a moderate aggregation of the nerve fibrils, which seem everywhere to underlie the ectoderm, and which in a few cases are gathered up into nerves. The under arm-nerve, which lies between the small arm-sinus and the surface, supplies nerves to the muscles of both arm-sinuses (figs. 22 and 28) . ”

“ In Megerlia it is three times attached, first to the hinge-plate, and then to the septum by processes from the diverging and reflected positions of the loop. In Magas the brachial skeleton is composed of an elevated longitudinal septum reaching from one valve to the other, to which are affixed two pairs of calcareous lamellae, the lower ones riband-shaped; attached first to the hinge-plate, they afterwards proceed by a gentle curve near to the anterior portion of the septum, to the sides of which they are affixed ”

“ The two lateral lobes contain the coelom; each separates off in front a segment which forms the head and presumably then divides again to form anteriorly the trunk, and posteriorly the tail regions. An interesting feature of the development of Chaetognaths is that, as in some insects, the cells destined to form the reproductive organs are differentiated at a very early period, being apparent even in the gastrula stage.
The great bulk of the group is pelagic, as the transparent nature of all their tissues indicates. They move by flexing their bodies. ”

“ Those who have not seen the animal in life, or who did not believe in the possibility of the valves crossing each other with a slight obliquity, would not consent to appropriating any of its muscles to that purpose, and consequently attributed to all the lateral muscles the simple function of keeping the valves in an opposite position, or holding them adjusted. ”

“ The interior of the head is filled up with masses of muscle fibres which are mainly occupied with moving the sickle-shaped hooks. The trunk contains a spacious body-cavity filled during the breeding season by the swollen ovaries, and the same is true of the tail if we substitute testes for ovaries. ”

“ The interior of the shell varies very much according to families and genera. On the inner surface of both valves several well-defined muscular, vascular and ovarian impressions are observable; they form either indentations of greater or less size and depth, or occur as variously shaped projections. In the Trimerellidae, for example, some of the muscles are attached to a massive or vaulted platform situated in the medio-longitudinal region of the posterior half or umbonal portion of both valves. ”

“ The eggs become very large, sometimes half the length of the mother; they are laid amongst water weeds. The male reproductive system is but little known, a small gland lying between the ovaries has been thought to be a testis, and if it be, the Gastrotricha are hermaphrodite. ”