500 EDWIN S. GOODRICH. 



Sagitta. 

 Archenteric diverticula give rise to the three pairs of coelomic 

 follicles present in the adult Sagitta. The genital cells are 

 precociously developed, and come to lie in the two posterior 

 pairs of follicles (Hertwig, 66). Whether the genital ducts — 

 which in the male segment, at all events, open into the coelom 

 by ciliated funnels — are peritoneal funnels, or are partly formed 

 from true nephridia, cannot be decided with our present in- 

 complete knowledge of their development. 



ECHINODERMA.^ 



Only a very brief reference can be made to this highly modi- 

 fied group. In the larva we find a right and left coelomic 

 follicle, the enteroccels (derived from unpaired or paired 

 archenteric diverticula), which may give rise to a second pair 

 of coelomic follicles by constriction. The anterior follicles 

 then develop peritoneal ciliated funnels (fig. 18), which 

 open to the exterior, fusing with paired epiblastic invaginations. 

 As a rule only the left peritoneal funnel becomes developed 

 (Field, 36; Bury, 20). The genital cells are developed from the 

 wall of the posterior coelomic follicles (MacBride, 75, 76) ; but 

 how far the genital ducts can be likened to peritoneal funnels 

 is quite uncertain. 



There appears to be no trace of true nephridia. 



Vertebkata.^ 

 As is well known, the coelom in the Vertebrates arises by the 

 hollowing out of a series of metameric blocks of mesoblast. 

 In the lower forms (Balanoglossus and Amphioxus) several of 

 the anterior coelomic follicles are formed directly as pouches 

 from the wall of the archenteron. From these follicles, pro- 

 duced by either method, peritoneal funnels are developed 



1 If the treatment of these last two groups (Echinoderma and Vertebrata) 

 seems to be somewhat too brief and dogmatic, it is that space will not allow 

 me to discuss the subject in exteuso. Moreover, we arc here treading on 

 such uncertain ground that I do not feel competent to treat of the structure 

 of these animals in full detail, and offer these remarks merely as a suggestion. 



