126 RITTER 



this parallel is perfectly fair. Diffuseness of the gonads is no 

 more a trustworthy index in this regard in the one case than in 

 the other. But should it be objected that Amphwxus and Bdello- 

 stoma are so much more remote from each other, taxonomically, 

 than are Balanoglossus and Ptychodera, that the comparison is 

 not altogether just, let us take another instance. In the genus 

 Poly car fa among the simple ascidians, the gonads in some of 

 the species are scattered widely over the mantle to which they 

 are attached in what are known as polycarps ; whereas in As- 

 ct'dia the gonad forms a somewhat lobulated, but yet a compact, 

 single mass. In short the gonads are diffuse in the one case, 

 and are not so in the other ; yet no one would conclude from 

 this that Polycarfa is a more archaic genus than is Ascidia. 

 I should not have expected that so excellent a morphologist 

 as Willey would have staked so much on this point, familiar 

 as he is with the wide differences to which the gonads are fre- 

 quently subject, even within the range of rather circumscribed 

 groups of animals. 



The truth of the matter is, as Willey himself has shown (see 

 his more recent and much fuller memoir, 1899), that the gonads 

 oiPtyckodera, like those of all other Enteropneusta, are w^ell de- 

 fined, more or less globular masses, each with its own envelop- 

 ing basement membrane, central cavity, and short duct opening 

 directly or indirectly to the exterior. And the only way in 

 which they are more diffuse in Ptychodera than in Balanoglos- 

 sus is that these masses are much smaller, probably in correla- 

 tion with the smaller size of the ova in the female, are much 

 more numerous, and more closely crowded in the former than 

 in the latter genus. 



On the whole, I am quite sure that so far as the gonads of 

 Ptychodera indicate anything regarding the ancestry of the 

 animal, they indicate it to be more highly modilied and hence 

 presumably older than Balanoglossus. One thing among others 

 pointing in this direction is the apparent fact that the gonadal 

 cavities, which are unquestionably primitive, are more com- 

 pletely obliterated in Ptychodera than in the Balanoglossida3. 



Concerning the exposed pharynx of Ptychodera flava and its 

 congeners, I would say that while I am not at all confident 



