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Show 1887.] ANATOMY OF EARTHWORMS. 375 boyeri \ The occurrence of such glands, however, is no more remarkable than their absence, and other genera are known (Acanthodrilus) in which such glands may be absent or present. The calciferous glands are present to the number of a single pair in segment 12 ; these glands are lobed, the furrows running parallel with the long axis of the body; they are lateral in position, but extend dorsally above tbe level of the oesophagus. The structure of these glands is closely similar to that which is found in other Earthworms ; they appear to be rather small in size compared to what they are (for example) in Acanthodrilus2 ; in the species of the latter genus investigated by me, the glands nearly fill up the body-cavity of the segments that contain them ; they are very far from doing this in Eudrilus. M. Perrier makes no mention of the presence of calciferous glands in any of the three species studied by him. In the tenth and eleventh segments, into which also open the funnels of the vasa deferentia, is a remarkable glandular body; this structure (Plate XXXIII. figs. 5 a, 6) consists of a median unpaired gland lying beneath the oesophagus, and evidently opening into it; in dissecting the worm it was necessary to raise the oesophagus, in order to bring into view these glands, which are completely hidden when the oesophagus is left in situ. These glands differ in their general appearance, as well as in their position, from the calciferous glands of the twelfth segme it, but do not differ in minute structure. The accompanying figure (fig. 3) illustrates the minute structure of one of these suboesophageal glands ; the section has been made through the oesophageal orifice, which is very wide. The lining epithelium of the gland differs in its character from the epithelium of the oesophagus, but there is no abrupt break between the two ; the epithelium lining the gland gradually passes into the epithelium of the oesophagus. The epithelial cells of the oesophagus are tall and columnar in form, very narrow at the base, and but slightly wider at the distal extremity ; on the other hand, the epithelium of the gland is composed of low cubical cells; the lining membrane of the gland is thrown into a series of folds which anastomose here and there; each fold contains a core of connective tissue in which are blood-vessels. The outer walls of the gland are of course in continuity with the muscular walls of the oesophagus, but their thickness is very considerably less. The serous coat of the oesophagus, as of the alimentary tract generally, is formed by a single layer of tall, pear-shaped peritoneal cells_the so-called " hepatic cells" (fig. 3, p); these cells, as in other Earthworms, contain numerous olive-brown, highly refracting particles in their interior. The fact that the base of the cell, where it is in contact with the wall of the alimentary tract, is prolonged into a stalk, which is hyaline and devoid of granules, and which rests directly upon the circular muscular layer, the longitudinal fibres being developed between the bases of the cells, probably gave rise to the erroneous supposition that these cells were glandules opening into the alimentary tract. This serous layer is continued over the « P. Z. S. 1886, p. 302. 2 P. Z. S. 1885, p. 811. |
