603 



"arise from the mesoblast cells in front of the septum" while Menon 

 thinks that they have their origin from the splanchnopleure, covering 

 the stomach and its diverticulum. Ike da describes a totally different 

 origin for these masses and says that they arise from "gigantic meso- 

 blast cells in the body cavity of the larvae with one or two pairs of 

 tentacles". Since the publication of his paper, however, Ikeda^ 

 has rejected this view but he has not as yet published anything on the 

 subject. 



There are two different Actinotrochae found in the waters of 

 Beaufort Harbor wich I shall designate as Species, A. (probably that 

 oi Phoronis architecta) and Species, B. Species, A., which is the smal- 

 ler of the two, is the more favorable for the study of the origin of the 

 blood corpuscles and in this form, the latter make their appearance 



Fig. 4. 



Fig. 5. 



■neyih.._ 



C.C.'- 



Vil.C. 



Fig. 6. 



-m.ij.c. 



b.c.Tn. 



Fig. 4. Transverse section through a young Actinotrocha with 12 tentacles. X440. 

 c.c, collar cavity; h.c.m, mesodermal blood corpuscle masses; neph, nephridium; tc, 



trunk cavity. 



Fig. 5. Section through mesodermal blood corpuscle masses. X1250. e.w, collar 



■wall; e.c.l, epithelial lining of collar wall; m.b.c, mother cell of blood corpuscles. 



Fig. 6. Same as Fig. 5. 



during the 14 tentacle stage. (The fully developed Actinotrocha of 

 this species has 18 tentacles.) 



Actinotrocha^ Species, A. with 16 tentacles invariably has blood 

 corpuscles and they are present in the so-called collar-cavity as two 

 masses more or less closely applied to the ventro-lateral wall of the 



8 Journ. of the Col. of Sc. Imp. Univ. Japan. Vol. 13. Pt. 4. 1901. 



40» 



