118 EDWIN S. GOODRICH. 



tends into the tentacles and into the pre-oral hood ; that in 

 front of the septum there is developed a second coelomic 

 cavity, in the form of a horseshoe-shaped canal, extending 

 into the base of each tentacle; that the nephridia open to the 

 exterior ventrally behind the septum, and project freely into 

 the pre-septal blood space, where they end blindly ; that this 

 inner extremity of the nephridium is furnished with a bunch 

 of typical solenocytes resembling those of Polychsetes and 

 of Amphioxus ; that during metamorphosis the pre-septal 

 coelomic canal becomes the pre-septal adult coelom, and that 

 the pre-septal hfemocoel becomes reduced to the adult ring- 

 blood-vessel ; that the nephridia lose their solenocytes and 

 their connection with the ring vessel, and acquire new open- 

 ings into the coelomic cavities, probably by means of ncAvly- 

 formed ccelomostomes or peritoneal funnels ; that the longi- 

 tudinal blood-vessels open into the pre-septal hasmocoel ; and 

 that a perianal sinus may be developed near the anal ciliated 

 baud. 



Much remains to be elucidated in the history of the 

 nephridia; and the origin of the cavities has not yet been 

 satisfactorily worked out. The possibility of the existence 

 at a very early stage of a separate pre-oral coelom, coming 

 into secondary continuity with the pre-septal h^emocoel 

 through the breaking down of an originally complete anterior 

 septum, has not been perhaps entirely excluded ; but, so far 

 as I am aware, there is no evidence in favour of the view that 

 such is the real history of the cavity of the hood. 



The existence in Actinotrocha of a closed nephridium pro- 

 vided with solenocytes is an interesting and important fact, 

 and its recognition enables us to add the Phoronidea to the 

 already long list of animals (Vertebrata, Annelida, Echiu- 

 roidea, Mollusca, Endoproctous Polyzoa, Nemertina, Rotifera, 

 and Platyhelmia) Avhose common ancestor must have pos- 

 sessed true nephridia of this nature. Wo may now expect 

 to hear of the discovery of flame-cells or of solenocytes in the 

 Sipunculoidea and Ectoprocta, which are doubtless related 

 to Phoronis. 



