:>GG MR FRANK E. BEDDARD ON THE ANATOMY OF OCNERODRILUS. 



This difference, which really distinguishes Claparede's two groups of Limicolso and 

 TerricolfiB, can hardly be due to the small size of the former group, for many of them 

 considerably exceed Ocnerodrilus, Microscolex, and some other forms in bulk ; it must 

 therefore have some importance. 



The only explanation that suggests itself to me is the need in terrestrial forms for an 

 especially thick cocoon to prevent evaporation and drying up of the contents ; a thin- 

 walled cocoon would be in this respect sufficient for those forms which live in water, or 

 particularly damp localities. On the other hand, it must be remembered that the 

 increased thickness of the clitellum in terrestrial forms is accompanied by an increased 

 specialisation in the cells. Benham figures four kinds of cells in the clitellum of 

 Microchceta, and the clitellum of other Earthworms seems to me to be equally com- 

 plicated. It is possible, therefore, that the structural diversity of the elements com- 

 posing the clitellum implies a physiological specialisation. The clitellum may perform 

 more functions than that of secreting the cocoon. 



§ Alimentary Canal. 



The first section of the alimentary tract is a very thin-walled buccal cavity, which is 

 evidently cajDable of being to a certain extent protruded at the will of the animal. In 

 one of the specimens studied by longitudinal sections the buccal cavity was slightly 

 everted, but did not actually project beyond the oral aperture ; its thin walls are attached 

 by comparatively few muscular strands to the parietes. It is these facts which lead me 

 to the inference that the buccal cavity can be protruded without the oral cavity, though 

 I did not notice anything of the kind in the living specimen. 



The pharynx immediately follows the buccal cavity, and occupies only a single 

 segment, the Illrd. It agrees in structure with the pharynx of many Earthworms, 

 having the usual mass of muscles upon the dorsal surface ; into this, as is also generally 

 the case, there project slight diverticula of the lumen of the alimentary tube. 



The oesophagus is a narrow tube, extending as far back as the end of the VHIth 

 segment. The lining epithelium consists of narrow columnar cells, which are covered 

 with a very thin chitinous layer. The lining membrane of the oesophagus is thrown into 

 irregular folds. Its muscular walls are tolerably thick. In segment IX the oesophagus 

 becomes widened out, and receives the ducts of a pair of glandular appendices (fig. Ad), 

 which lie in this segment. These structures evidently correspond to the " sac-like 

 appendices" of which Eisen has recorded the presence in Ocnerodrilus occidentalis ; 

 they seem, however, in my species to be situated a segment further back. Eisen has 

 stated that there is no structure in the Limicolse with which these glandular diver- 

 ticula can be compared. I am inclined, however, to compare them with the " Chylus 

 Taschen " of the Enchytraeidse on the one hand, and with the calciferous glands of the 

 terrestrial Oligochaeta on the other. Among the Lumbriculidse they do not appear to 

 have any equivalent. 



