116 EDWIN S. GOODRICH. 



finally to become separated into two blind tubes projecting 

 into the pre-septal heemoco}!, and opening to the exterior. 

 " Besides," writes Ikeda, " a certain number of mesenchy- 

 matous cells, which later undoubtedly become the excretory 

 cells of Actinotrocha, are always found attached to the blind 

 ends of the nephridial canals." I feel convinced that these 

 so-called mesenchymatons cells are the cells described by 

 Caldwell, and really derived from the epiblastic invagination. 



An accurate and detailed account of the origin of the 

 solenocytes of Actinotrocha is still wanting. Should the 

 nephridia prove to be actually developed from the epiblast, 

 this origin and their ascertained relation to the ha3mocael 

 would be welcomed as two more nails in the coffin of that 

 theory according to which the nephridia are parts of the coelom. 



Another hardly less uncertain and perhaps even more 

 important question which remains to be settled concerns the 

 fate of these nephridia after metamorphosis. 



It is well known that there are in the adult Phoronis two 

 organs opening near the anus, which communicate with the 

 post-septal trunk ca3lom by means of wide open ciliated 

 funnels. In some species, at all events, a similar opening- 

 occurs into the pre-septal coelom — as in Phoronis australis 

 (Benham [1]). These organs, generally called the nephridia, 

 function both as excretory and as genital ducts. Now it is 

 clear that, if they in any way represent the nephridia of the 

 larva, they must have lost their primitive connection with 

 the pre-septal blood-vascular ring, and have acquired new 

 openings into the cuuloraic cavities. Since it is generally 

 agreed that no trace of a second pair of excretory organs 

 occurs in the larva, the (piostion we have to decide is hoAV far 

 the adult organs are due to new formations, and how far to 

 the modification of the larval nephridia during or after 

 metamorphosis. 



Caldwell describes how, at metamorphosis, " the larval 

 excretory cells of the nephridia break off from the large 

 canal and iloat freely in the body-cavity in front of the 

 septum. They pass with the blood-corpuscles into the vessels. 



