MOEPHOLOGT OF THE PEDIPALPI. 45 



we must regard both the Crustacea and the two sections of 

 Araclinida as having for their common ancestor a form with 

 nephridia in each segment. 



The Gut. 



The only point on which I wish to make a few remarks in this 

 connection is the origin of the stercoral pocket as I have described 

 it above. There is no doubt in my mind that in Phrynus it is 

 formed from the mesenteron. The position of the Malpighian 

 tubes, which I discovered after I had completed the section 

 dealing with Pkrynus, as running in close contact with the wall 

 of the stercoral pocket, to open into it at its posterior end, 

 is absolutely conclusive, though the evidence from histological 

 structure and anatomical relations in PJirynics and Thelyphonus 

 was pretty strong already. In Spiders, however, it is always 

 described as being formed from the proctodseum ; and the question 

 arises whether the stercoral pocket in Spiders is not analogous 

 with that of Pedipalpi, or whether the development has not been 

 properly described. I incline to the latter view. That the deve- 

 lopment of this part of the gut is not quite straightforward is, I 

 think, evident from the fact that Kishinouye *, in his elaborate 

 paper on the development of Araneina, describes it as formed from 

 the unpaired caudal coelom. Such a startling suggestion as this 

 certainly requires independent confirmation, and I think that 

 possibly Kishinouye has mistaken the early formed posterior part 

 of the gut for coelom. However this may be, Kishinouye's figures 

 seem to make it pretty clear that the stercoral pocket has no 

 connection with the proctodseum, which at this stage is represented 

 by a solid plug of cells, just as it is in Phrynus. The formation 

 of the Malpighian tubes in the Spider has also never been quite 

 satisfactorily described, and if they run in close contact with the 

 stercoral pocket, as they do in Phrynus, they might easily be 

 mistaken as opening into the anterior end of the pocket. Kishi- 

 nouye admits that he is not satisfied with his observations on the 

 origin of these structures, and the description by other observers 

 is hardly more satisfactory than his. Locy's description t is brief, 

 and his figures are capable of a different interpretation to that 

 which he gives them : fig. 57, in particular, seems rather in favour 



* Journ. Coll. Sci. Jap."' 



t EuU. Mus. Comp. Zool. Harvard, xii. 



