EKOBNT WOT^K ON THE PROTOOHORDA. 227 



The fact that Ptychodera flava clears away this difficulty 

 is alone sufficient to entitle it to be regarded with particular 

 respect. This remark no doubt applies to the sub-genus 

 Chlaniydothorax to which Pt. flava belongs. 



In most Ptychoderidae the lateral septa, as described by 

 Spengel, have a limited anterior extension; the point of their 

 proximal or mesial origin from the basement membrane gra- 

 dually approaches that of their distal insertion into the same 

 membrane until the two points coincide ; and so the lateral 

 septum on each side comes to an end in the posterior branchial 

 region. In this way there actually exists a portion of the coelom, 

 bounded mesially by the dorsal mesentery ^ and laterally by 

 the lateral septum, which ends blindly in front ; and as long as 

 this was all that was known on the subject there was perhaps 

 no other alternative than to propound some such formal ex- 

 planation as that put forward by Spengel. 



In Ptychodera flava the lateral septa do not come to an 

 end in the posterior branchial region, but they are co-extensive, 

 in front and behind, with the genital pleurae. It can therefore 

 hardly admit of question that the genital pleurae and lateral 

 septa are causally related to one another. 



Where the genital pleurae are at their maximum the lateral 

 septa are entire. As the genital pleurge have become reduced, 

 the reduction always taking place from before backwards, the 

 the lateral septa have been subjected to the same process of 

 limitation, and exhibit the effects of it in a more marked 

 manner. 



MM. Delage and Herouard do not devote much space to the 

 difficult subject of excretion in the Enteropneusta, being con- 

 tent to state that tlie essential organ of excretion is the 

 glomerulus which forms part of the central complex of the 

 proboscis, while the excretory products are said to be got rid 

 of through the proboscis-pore. 



1 This holds good only for the post-branchial region. In front of the last 

 gill-cleft on each side, the proximal origin of the lateral septum is transferred 

 from the wall of the gut to the basement- membrane of the epidermis. 



