040 T. IKE DA : 



view of the Ixjdy-divisions. The external appearance of the three 

 ]iortions I have already descril^ed in brief. As to the internal body- 

 cavities corresponding to tliese external portions, I can not agree 

 with Masterman, when he says that they are completely separated 

 from one another ; for, as I shall soon show, the septum which lies 

 between the preoral and the collar cavities is always an incom- 

 plete formation, at least in all the Adinotrochœ which I have 

 observed. Besides, T have been unable to detect the first and third 

 pairs of nephridia, which are said to exist in the preoral, and the 

 trunk cavities (Master^afan). Therefore, I can not regard the body- 

 divisions 0Î Actinotrocha as " segments " in the sense ofthat author. 



The septa or mesenteries are very delicate in structure and 

 can hardly be recognized in living specimens. I have, therefore, 

 had to study them mostly in sections. I shall hereafter call the 

 two septa the preoral, and the postoral, septa. 



Larval Preoral Body-Cavity. The larval prcoi'al l)ody-cavity 

 fills u]) the interior of the hood, in which there is no entoblastic 

 organ. Innumeral)le mesench\miatous filtres traverse the cavity 

 (figs. 45, 49, 63 a, m./.). A few blood corpuscles are also 

 frequently discovered in this cavity (fig. 49, corp.) ; this fact is, 

 I believe, one of the proofs of the correctness of the view which I 

 now propose to consider. 



I have already spoken of the incomplete formation of the preoral 

 septum. Whether this is a mere sjiecific difference or not, remains 

 to me uncertain, as I have had no chance of examining the larvae 

 investigated by Masterman. In sagittal sections of the larva at 

 any stage of its growth, the septum can constantly be traced so 

 long as the œsophagus is contained in the sections. In figs. 4ô 

 and 63 a, a slender cellular strand {mes'.) behind the ganglion {gl.) 

 represents the septum in cross section. It extends between the 



