THE SLIME- AND THE CRURAL GLANDS. 195 



such as those of the Alciopinac. According to Kleinenbeeg (A r ol. i., p. 289, 

 Annelidan Lit., No. 26), the eyes in this family arise independently of the 

 cephalic ganglion as two ectodermal invaginations, but the inner wall of the 

 optic vesicle is said to become closely connected with the brain, giving off cell- 

 material direct to the latter. The elements of the two organs, in any case, 

 seem for a time to be closely united, at the very point where the optic nerve 

 forms later. If Kleinenbeeg's observations are confirmed, a similar condition 

 might be thought to prevail in Pcripatus also, and the opposing views of 

 v. Kennel and Sedgwick might thus be explained. 



The Slime- and the Crural Glands. 



The slime-glands are of ectodermal origin, arising as depressions 

 on the tips of the oral papillae (Fig. 93). At first the pits are 

 shallow, but they gradually deepen and their blind ends grow inwards 

 and backwards. The pit has thus, at the stage depicted in Fig. 

 94 B, become a conical tube (Fig. 97, sd), which has grown back 

 to the intestine. This growth continues in the following stages, so 

 that the glands eventually attain a considerable length. They 

 retain their simple tubular form; the branches which occur in 

 them in the adult appear as outgrowths shortly before the embryo 

 is mature and ready for birth (v. Kennel). 



The slime-glands are no doubt to be regarded as modifications of 

 the crural glands, which, as sac-like structures, lie in the lateral 

 divisions of the body-cavity and open on the ventral side of the 

 feet. In the different species of Peripatus they differ in number 

 and in distribution. These glands first appear at a late stage of 

 embryonic development as ectodermal invaginations lying at the 

 bases of the feet distally to the apertures of the nephridia (Fig. 

 102, c, Sedgwick). In the male (P. capensis) the crural glands of 

 the last pair of feet are transformed into long glandular tubes 

 (Balfour). 



The Alimentary Canal. 



With the exception of the short stomodaeum and proctodaeum, 

 which are ectodermal derivatives, the alimentary canal is of ento- 

 dermal origin. 



The following account is derived principally from the description given by 

 Sedgwick of P. capensis, this form being chosen because we must regard it as 

 more primitive than the American species examined by v. Kennel. The two 

 forms vary principally in the first stages of the development of the intestine, 

 the later stages showing great similarity. 



In order to understand the formation of the intestine, we must 

 revert to the gastrula stage of P. capensis. The blastopore there 

 leads into a cavity, which is lined by a thick protoplasmic 



