DISCOPHORA. 293 



spond with the segments. In the adult however the anterior lobe is 

 really double and has two divisions for the two segments it fills, while 

 the posterior lobe, which, as is well known, extends backwards parallel 

 with the rectum, is composed of five segmental sacculatious. In 

 connection with the stomodaeum a protrusible pharynx is developed. 

 In Hirudo and Nephelis the mesenteron has from the first a 

 sack-like form. The cells which compose the sack give rise to 

 a secondary deposit of food-yolk. The further changes are practically 

 the same as in Clepsine. In Hirudo the posterior sacculation of the 

 stomach is primitively unpaired. The jaws are formed at about the 

 same time as the eyes as protuberances on the wall of the oral cavity. 



BIBLIOGRAPHY. 



(359) 0. Biitschli. "Entwicklungsgeschicktliche Beitriige (Nephelis)." Zeit.f. 

 wiss. Zool. VoL xxix. 1877. 



(360) E. Grube. Untersuchungen HI), d. Entwicklung d. Anneliden. Konigsberg, 

 1844. 



(361) C. K. Hoffmann. " Zur Eutwicklungsgeschichte d. Clepsineen." Nieder- 

 Icind. Archiv f. Zool. Vol. iv. 1877. 



(362) B. Leuckart. Die mensclilichen Parasiten (Hirudo), Vol. i. p. 686, et seq. 



(363) H. Bathke. Beit. z. Entwicklungsgesch. d. Hirudineen. Leipzig, 1862. 



(364) Cb. Bobin. Mem. sur le Developpement ernbnjogenique des Hirudinees. 

 Paris, 1875. 



(365) C. 0. Whitman. " Embryology of Clepsine." Quart. J. of Micro. Science, 

 Vol. xvin. 1878. 



[Vide also C. Semper (No. 355) and Kowalevsky (No. 342) for isolated observations.] 



