792 PROFKSSOR J. STEPHENSON 



The condition (fig. 2) has here not advanced quite so far, but the changes are 

 essentially the same. The buccal cavity is patent for a short distance from the 

 mouth opening, but is quite shut off from the pharynx. The pharynx appears as a 

 closed ovoid sac, the lining epithelium of which still appears dorsally as a layer of 

 columnar cells, but ventrally is not so high and is losing its cellular character ; the 

 interior is filled with debris. On the dorsal side of the pharynx, outside the 

 muscular layer, is a considerable mass, in which cell outlines are no longer to be 

 made out. 



The oesophagus is a narrow band, quite impervious, showing numerous nuclei and 

 longitudinal muscular fibres. Behind the genital segments the gut, though still 

 narrower than normal, and no longer dilated between the septa, becomes pervious 

 again — at least in places, though it is largely blocked by epithelial debris. The 

 epithelium of the intestine is much altered, and shows intense degenerative changes. 

 It is lower than normal, and the cells are often largely vacuolated ; sometimes 

 granular inclusions are present in the vacuoles, at other times they appear empty ; 

 in some cases the nucleus only is left, in a large empty space, ami it also may be in 

 process of losing its staining power. Many degenerate cells appear to have loosened 

 themselves from their attachment, and help to block the lumen of the canal. 



The condition may be compared with that described for H&monais laurentii 

 (p. 779 ante) ; the atrophy of the canal is here even more profound than there. 



The curious degeneration of the alimentary canal in the sexual animal, here de- 

 scribed, has not so far been met with, I believe, in the Oligochceta. In the Polychaeta 

 a somewhat similar condition has been found in a number of families ; the data have 

 been summarised by Potts (" Methods of Reproduction in the Syllids," Ergeb. u. 

 Fortschr. d. Zoologie, vol. iii, 1913), from whose paper the following facts are taken. 

 Thus, among the Syllids, the sexual forms of Odontosyllis show no modification of 

 pharynx and proventriculus, but the intestine undergoes a certain shrinkage in size, 

 and signs of cellular degeneration are seen in sections ; in Autolytus maculatus, in 

 the latter stages of the growth of the gonads, there is a corresponding shrinkage of 

 the alimentary canal ; the same has been observed in Exogone. In other families 

 Glycera capitata, Palolo viridis, and various Phyllodocidse undergo a similar change. 

 In Notomastus Uneatus the degeneration of the intestine leads first to an elongation 

 of the tube, in consequence of which it is thrown into numerous windings ; the cell 

 boundaries become obscure, the nuclei increase in number, globular highly refracting 

 bodies appear in the cytoplasm, and the epithelium is finally reduced to a single 

 layer of plate-like cells only 2 m thick. In Dodecaceria concharum the diameter of 

 the gut is markedly reduced ; there is always a continuous epithelium, but the 

 number of cells is reduced enormously. In neither of the last two cases can the 

 atrophy of the intestine be attributed to the pressure of the genital products. 



In Dero the atrophy goes much further than in any of the above instances. The 

 mouth aperture disappears, and the buccal cavity, pharynx, and oesophagus, as well 



