Frank E. Beddard

“ The oxygenation of the blood probably takes place to some extent through the walls of the oral fringe, but the blood which receives its oxygen at this spot is limited in its distribution, and could only supply the brain and head. It seems probable that the remaining organs are supplied with oxygen by the fluid of the body-cavity, which bathes them on all sides. This might obtain its oxygen from the blood in the heart, or more probably, through the thin walls of the intestine, from the stream of water which is maintained by the ciliated groove described above. ”

“ Outside is the epidermis, which always consists of a single layer of cells, except in the clitellar region of earthworms. It is a point of difference between the aquatic genera and the terrestrial forms that in the former the clitellum is only one cell thick, while in the higher Oligochaeta it is made up of more than one layer of cells. The epidermis is ciliated only in the genus Aeolosoma, and there only on the prostomium. It secretes a thin layer of chitin, which is defective opposite to the glandular cells, and becomes therefore perforated by numerous pores. ”

“ The embryos are hatched out within the uterus, and the larvae leave the body of the mother through the generative pore. The minute larvae bore through the intestinal walls of their host, and then, either burrowing in the tissues or swept along in the stream of blood or lymph, make their way all over the body, and come to rest most usually in the muscles, but occasionally in other parts. When the larva reaches its resting-place, it either pierces the sarcolemma and establishes itself within the substance of the muscle-fibre, or it comes to rest between and not in the fibres. ”

“ This cavity, common to all the higher animals, is known as the coelom; it is lined by cells, which cover the intestines as well as the inside of the body-wall; and upon the intestine assume the form so characteristic of the group, namely, that of large yellow cells loaded with secreted matters, and called "chloragogen-cells" by Claparède. The coelom communicates with the exterior by means of the dorsal pores, the nephridia, and the ducts of the reproductive organs. As in all animals which possess a coelom, the reproductive tissues, ova and sperm, are developed on its walls. ”

“ Leptoplana employs two kinds of movement, creeping and swimming. Creeping is a uniform gliding movement, caused by the cilia of the ventral surface, aided perhaps by the longitudinal muscular layers of this surface, and is effected on the under side of the "surface-film" of water almost as well as on a solid substratum. Swimming is a more rapid and elegant movement, employed when alarmed or in pursuit of prey. The expanded fore-parts of the body act as lobes, which are flapped rapidly up over the body and then down beneath it, undulations running rapidly down them from before backwards. ”

“ Let us now imagine the condition we should have if a large and continuous cavity were developed between the alimentary canal and the body-wall. The body-wall would clearly have the general relations of a zooecium, while the alimentary canal and tentacles would obviously correspond with the polypide. The existence of the body-cavity would make it possible for the animal to retract its tentacles instead of merely turning them in. Regarded in this way, there is but little difficulty in comparing the Ectoprocta with the Entoprocta. ”

“ The red- or forked-worm, Syngamus trachealis Sieb., is common in poultry and game birds, and causes the disease known as gapes, which is especially common in young birds, and often gives rise to extensive loss. The peculiarity of this genus is that the male is permanently attached to the female, its genital bursa being so closely adherent to the opening of the oviduct that two specimens cannot be separated without tearing the tissues. The ova are not laid, but escape from the body with fully-formed embryos in them, by the decay or rupture of their parent's body. ”

“ In the young Priapuloidea the duct with its branching canals is not masked by the generative organs, but as the animals become mature, diverticula from the duct arise, and the cells covering these become modified into ova in the female, and into spermatozoa in the male. The presence of these follicles masks the excretory part of the gland. The ova and spermatozoa escape through the ciliated ducts which open to the exterior one on each side of the anus, and, contrary to what is the case with other Gephyrea, leave the body without having ever been in the body-cavity. ”

“ The nervous system consists of a ventral cord lying in the body-cavity, as in the Sipunculoidea, but attached to the skin, and of a circumoesophageal ring. With the growth of the proboscis this ring is drawn out, and the two branches run along the sides of the proboscis and unite at the tip. There is no specialisation of brain, nor are any special sense organs present, but the ventral cord gives off paired nerves at regular intervals, which, uniting dorsally, form rings in the skin in some and probably in all species. ”

“ There are various considerations which enable us to form a fair opinion as to the probability of a given species being really indigenous or imported. Oceanic islands afford one test. There are species of earthworms known from a good many, but with a few exceptions they are the same species as those which occur on the nearest mainland; in those cases where it is supposed that the animal inhabitants have reached an oceanic island by natural means of transit, it is a rule that the species are different, and even the genera are frequently different. ”

“ It is a common parasite in man, and has been found in the ox. It is now generally recognised as the same parasite which inhabits the pig, and which Dujardin regarded as specifically distinct, and named A. suillae. In the latter host, however, it never attains the dimensions it does in man. It inhabits the upper and middle parts of the small intestine, and has been known to escape into the body-cavity and set up abscesses there, or to make its way into the stomach, and to be voided through the mouth. ”

“ The eggs and spermatozoa in the Polychaeta are discharged into the sea either by rupture of the body-wall or through the nephridia; the male and female elements unite, and the resulting fertilised eggs undergo development, either floating separately in the water, or embedded in jelly, or attached to the body or to the tube of the worm. ”

“ It is not therefore surprising that a "zone of budding" arises in an uninjured worm at certain seasons, viz. that of reproduction; it is a property that each worm possesses, though generally it remains latent till injury provides the stimulus.
Moreover, not only can new segments arise at the hinder end, but a new head can be formed at the anterior end, as has been observed in worms belonging to many families—in the less modified Syllidae, [338] in others of the Nereidiformia, and even in Sabellids, where the greatly specialised gill filaments can be reproduced. ”

“ The nervous system lies entirely in the epidermis. The body-cavity is regularly segmented by transverse septa passing from the body-wall to the intestinal wall. The foregut presents a slight eversible portion in Polygordius, whilst in Protodrilus it has a peculiar U-shaped muscular diverticulum on its ventral surface, corresponding with the similar apparatus in Dinophilus; it is capable of eversion, and aids the worm in burrowing, as well as in seizing and swallowing the mud. The vascular system is represented by a dorsal and a ventral vessel, neither of which, however, is contractile. ”

“ Female Reproductive Organs.—The ovaries of the Hirudinea appear to differ from those of the Oligochaeta in that the ovaries are continuous with their ducts. In Hirudo, however, the real ovary of each side consists of masses of germinal tissue lying freely within a sac which communicates with a duct; the two ducts unite to form a much convoluted tube which opens into a thick-walled vagina, itself opening again on to the exterior by a median unpaired opening on the seventh segment. The muscular vagina is not always present. ”

“ Their elongated thread-like bodies afford little resistance to the passage of the food, which, as it passes through the intestine of the host, might tend to carry the parasites out of the body. At the same time their shape enables them to pierce and wriggle through the various tissues without making any very serious lesions such as might prove fatal to their host. Their extraordinary power of resisting desiccation both in the egg and in the adult state vastly increases their chances of ultimately hitting on the right host. ”

“ In Cristatella we have the most highly modified of all the Phylactolaemata. The individuality of the zooecium is here subordinated to that of the colony as a whole. The branched arrangement of the zooecia is greatly obscured. The body-cavities have become completely confluent, although rudiments of the septa still exist. The ectocyst has been lost, with the exception of the basal layer of the colony. The tentacles are more numerous (80-90) ; and in accordance with the increase in the elaboration of the genus, its statoblasts belong to the most complicated type known. ”

“ As, however, but one species of Eudrilus is found out of Africa, and as that species is so common in gatherings from various tropical countries, it seems to be an instance of a species with large capacities for accidental transference from country to country. The type genus, Eudrilus, has been known since 1871, when it was originally described by M. Perrier. [446] Since that date nineteen other genera have been described from Africa by Dr. Michaelsen, Dr. Rosa, and myself. The most salient external character of the group, not universal but general, is the unpaired male and female orifices. ”

“ In Nereis there is in each segment, in addition to the pair of nephridia, a pair of "dorsal ciliated organs" (Goodrich) (cil.org in Fig. 124) . Each appears as a wide-mouthed funnel, greatly folded, and without any permanent outlet. But it is possible that these organs function as genital ducts, and that the external aperture will make its appearance temporarily at the period of maturity. This "dorsal ciliated organ" has not been met with in allied genera—such as Eunice, Nephthys, Polynoë, Glycera—where the nephridium is a wide tube, and serves as a genital duct. ”

“ From this great and unnatural group, which has survived as "Vermes" even in some quite modern text-books, we can separate off those forms which show a plain segmentation or division of the body internally as well as externally into a series of more or less similar rings, as a Class Chaetopoda. This Class, consisting of the Orders mentioned on p. 241, includes the worms which form the subject of the present chapter—the Oligochaeta, as they were originally called by Grube, on account of the fewness of their chaetae as compared with the number possessed by the majority of the Polychaeta. ”