ROTIFERA. 413 canal is constructed into a bag or stomach, as Brachionus.
4. Trachelocystica, with a simple alimentary canal, enlarged at the lower part, as in Rotifer.
The upper part of the alimentary canal be low the jaws is called by Ehrenberg the ceso phagus, and is said to be either long or short, according to the distance which intervenes between the jaws and the further enlargement of the alimentary canal. In some cases, as in Stephanoceros (fig.292. c), there is an enlarge ment anterior to the origin of the jaws, which is called the crop or gizzard. Into this cavity the food is taken before it passes into the lower portions of the alimentary canal. The same organ is seen in Floscularia. In this animal it is evidently clothed with vibratile cilia, whose movements seem to make up for the deficiency of a true rotatory apparatus. The whole of the alimentary canal seems to be lined with vibratile cilia, for although they are too minute, in most instances, to be seen, yet the movement of objects in the interior of the canal, as well as the force and direction with which substances are occasionally pro pelled from the oral orifice, would lead to this conclusion. The whole of the alimentary canal is often inclosed in a mass of cellular substance, as seen in Philodina roseola (fig. 295. c), and Dinocharis paupera (fig. 302.).
Fig. 303.
Notommata myrmeleo.
a, the single eye ; b, oesophagus ; c, alimentaiy canal; d, d, muscular fibres; e, e, glands; f, f, re spiratory processes; g, sexual tubes (male ?); n, germinal vesicle in ovum; i, ovarium ; b, vascular network.
Attached to the intestinal tube, and ap parently enlargements of its walls, are various appendages, about whose functions there is much difference of opinion. The most con stant of these bodies are seated on each side of the termination of the ccsophagus. They are mostly two in number, one on each side (fig. 297. c, c ; fig. 289. c,c ; fig. 296. h; h.) Sometimes they are four in number, as in No tommata myrnzeleo (fig. 303. e, e), and in other cases more numerous. Ehrenberg originally regarded these as spermatic glands, but, sub sequently, he called them pancreatic glands. Grant and others have called them indif ferently pancreatic or salivary glands ; and if they are secreting organs at all, they probably perform the functions of these glands in higher animals. Seated lower down the alimentary canal than these, are sometimes seen other projections, having the appearance of follicles, and these have been supposed to secrete bile. Dr. Grant describes what we have called a cellular mass in Philodina roseola, as a number of " short, straight biliary follicles," such as are seen in many of the higher forms of Annelides. Professor Rymer Jones re
gards the superior as well as the lower of these appendages, as the " first rudiments of a liver." Dujardin is inclined to regard these appendages rather as creca than glands.
Vascular and respiratory systems. — Al though Ehrenberg has pointed out several structures in the Rotifera as indications of a vascular system, it is very questionable whether any circulation takes place through vessels at all. In Hydatina senta (fig. 293.), Notommata myrnzeleo (fig. 303.), Rafter vul garis (fig. 299.), and many others, can be seen a series of transverse bands, lying directly under the tegument ; in Hydatina senta, these are connected with a longitudinal band, and these are regarded as a dorsal vessel and its branches. Doyere, with much propriety, re gards these as a musculo-cutaneous system, analogous to a system of the same kind which lie has described in the tardigrade Infusoria. In Hydatina senta, Notommata myrmeleo, and some other species, there are some free longitudinal cords, connected with a fine vascular network near the mouth, and which send filiform prolongations to the ali mentary canal, which Professor Owen thinks may, with more probability, be regarded as " sanguiferous organs." We must, however, express our doubts as to the existence of a vascular system in these animals at all. In some of the Rotifera, internal tubes are seen, called by Ehrenberg seminal tubes, and upon these are often placed a row of little project ing tremulous processes, on which he has be stowed the name of gills. These processes are not very numerous in Hydatina senta (fig. 293.) ; but they are more numerous in Notommata myrzneleo (fig. 303. f, f). The tubes on which these gills are placed, com municate in some instances with vessels at the back part of the neck, which are again in relation with the siphon to which we have before alluded, and the whole is supposed to constitute the rudiments of a respiratory system. Whatever may be the true function of these parts, it cannot be supposed that the oxygenation of the nutritive fluid, takes place entirely in these organs. Not only is the alimentary canal supplied with vibratile cilia, but its peritoneal surface, and the cavity in which it is placed, so that on these surfaces the respiratory changes might take place quite independent of these organs. Dujardin refers the office of certain contractile vesicles (fig. 297. b ; fig. 288. a.), regarded by Ehrenberg as connected with reproduction, to the respira • tory function.