72 



Dr. H. P. CJowlcs on the Bodij-cavilies and 



presence of a nioseiiteiy between tlio cavity of the preoral 

 lobe and that of tlie colhir. Longchamps, Ikeda, and Good- 

 rich ao[ree that this structure is incompU^te, and the former 

 considers it to be a secondary structure. Menon, and probably 

 Masterman, on the other hand, consider it to be a complete 

 mesentery, 



I have studied the two Actinotrochce found in the liarbour 

 of Beaufort, North Carolina, and I am inclined to think that 

 one of these is the Actiuotrocha of Phoronis architecta. In 

 both species there is an inconiplcte mesentery between the 

 preoral lobe and the collar-cavities and a complete one 

 between the collar- and trunk-cavities. The trunk-cavity 

 contains a ventral mesentery, and in one species indications 

 of a dorsal mesentery, but there is no sign of a dorsal mesen- 

 tery such as Masterman describes for the collar-cavity. 



There seems to be more or less inclination on the part of 

 those who have investigated the Adinotrocha since the appear- 

 ance of Masterman's paper to doubt the correctness of the 

 latter's observation as to the five-fold origin of the body- 

 cavities from the euteron. 



Fi?. 1. 



...mjis. 



Sagittal spction tln-migh gastrula of Plioronis architecta, X 704. 

 y., ganglion ; h.l., blastopore ; m.p.s., mesodermal preoral sac. 



I do not find that the origin of the mesoderm in Phoronis 

 architecta agrees with Masterman^s account for Phoronis 

 Buskii, nor do I find that the mesoderm arises from archenteric 

 diverticula. My observations agree more closely with those 



