228 ARTHUR WILLEY. 



Batesou^ found granules in nearly all the mesoblastic tissues, 

 and he says (p. 526) " they may perhaps be excretory, and it 

 is possible that they are more or less removed by the proboscis- 

 pore and collar-funnels respectively. This does not explain 

 their presence in large masses in the trunk body-cavity, from 

 which no pore has been observed to open/' 



In the first place it should be remembered that it is not ab- 

 solutely necessary that excretory products must be removed 

 from the body; this is shown in the Ascidians, where there 

 are no excretory ducts. The so-called pericardium (Herzblase) 

 of the Bnteropneusta which lies in the centre of the glomerulus, 

 i.e. between the two halves of the latter, appears, from the 

 curious way in which its endothelium proliferates into the 

 cavity (to such an extent as sometimes to completely block up 

 the cavity), to stand in functional as well as in topographical 

 relation to the glomerulus. If this is so, it would, in its 

 capacity as a closed sac associated with the renal function, be 

 physiologically comparable to the organ of Bojanus of the 

 Molgulidse. 



The glomerulus of the Enteropneusta is, so far as our present 

 knowledge goes, a structure sui generis,and itis quite clear that 

 it is the principal organ of excretion only in virtue of its having 

 superseded something else, namely the paired excretory canals. 



The proboscis-pores are highly variable ; the collar-pores are 

 constant; but neither the former nor the laiter are any longer 

 mere excretory pores. The collar-pores especially seem to 

 promote locomotion by taking in water, and so causing the 

 collar to swell (Spengel) ; this may happen also in the case of 

 the proboscis-pores sometimes, but not always. 



I have observed what 1 believe to be the vestiges of a pair 

 of truncal canals and pores in two species of the genus Spen- 

 o-elia. In both Sp. porosa and Sp. alba, n. sp., there is a 

 pair of canalicular extensions of the first pair of gill-pouches 

 into the posterior end of the perihsemal cavities close to the 

 level at which the latter pass into the truncal coelom. They 

 occur a))i)roximalely at the same level as the collar-canals, 

 • 'Quart. Journ. Micr. Sci.,' vol. 2G, 1S8G. 



