599 



ActinotrocJia corresponds, in the form I have worked on, to that of the 

 Actinotrocha immediately after metamorphosis. 



Some of the early investigators recognized the presence of a 

 hlood vessel along the dorsal wall of the stomach and also masses of 

 blood corpuscles. 



Me tschnikoff^ and E. B. Wilson* observed that the cavity 

 containing the blood corpuscle-masses gives rise to the ring-vessel of 

 the adult and the later papers of Caldwell and Ikeda confirm their 

 statement. 



While Masterman describes a much more complicated vascular 

 system for the Actinotrocha from St. Andrews Bay than that of all the 



Actinotrochae I have examined, yet I 



agree with his view that the cavities of 



P^ç- y^^SSlìììì^ ^^^^ blood vessels may be considered as 



vestiges of the segmentation cavity. 



Fiff. 2. 



Fis. 1. 



Fig. ]. Longitudinal section through an Actinotrocha which is almost ready to me- 

 tamorphose. X225. a.c.c, adult collar cavity; l.c, blood corpuscle; c.c, collar cavity; 

 e.c.l, epithelial lining of collar wall; m^, mesentery between collar and lobe cavities; 

 m2, mesentery between trunk and collar cavities; p.l.c, cavity of preoral lobe; t.h.v, 



tentacular blood vessel of adult; t.c, trunk cavity. 



Fig. 2. Transverse section through the collar segment of an Actinotroclia. X 225. 



a.c.c, adult body cavity; h.c, blood corpuscles; c.c^ collar cavity; J.a, digestive area; 



d.v, dorsal blood vessel; e.c.l, epithelial lining of collar wall; nfi, mesentery between 



collar and trunk cavities; ìieph, nephridium; t, tentacles; t.c, trunk cavity. 



The blood vessels of the adult in the Actinotrochae from Beaufort 

 Harbor are represented by a dorsal blood vessel (Fig. 2 cl.v] running 

 along the median line of the stomach from the dorsal insertion of the 



3 Zeitschr. f. wiss. Zool. Vol. 21. 1871. 



4 Quart. Journ. Micr. Sc. Vol. 21. 1881. 



