605 



rudiment of the young adult body cavity yet I am convinced that they 

 do not give rise to it. 



In Species, A., there is no intimate relation between the masses 

 of blood corpuscles and the nephridia such as has been described by 

 Masterman for the species from St. Andrews Bay and by Long- 

 champs^ for Actinotrocha hranchiata. In the larva of 16 tentacles 

 the blood corpuscles, however, are closely applied to the stomach wall 

 in the region of the digestive area. There is no mesodermal epithelium 

 covering that part the surface of the stomach which lies within the 

 collar-cavity, and the blood corpuscles seem to be so intimately related 

 to the digestive areas that I am inclined to believe that they receive 

 nourishment from them (Fig. 2). 



While the blood corpuscles vary in size and undoubtedly multiply 

 by karyokinetic division yet I 

 have never found the "large 

 and somewhat coarsely granu- 

 lar" and the "smaller finely gra- 

 nular" corpuscles that Iked a 

 speaks of nor in this species have 

 I found any "gigantic meso- 

 derm cells" in the region of the 

 blood corpuscle-masses. Very 

 large cells in close relation to 

 the blood corpuscle-masses are 



da. 



Fig. 7. Transverse section through the di- 

 gestive area of an Actinotrocha. x 450. 5.c, 

 blood corpuscle; c.w, collar wall; d.a, dige- 

 stive area; g.m.c, gigantic mesoderm cell. 



found in some specimens of -4c^mo^rocÄa, Species, B. (Fig. Ig.m.c). These 

 cells resemble those which are present in the old gastrula of Species, A. 

 and which arise from the wall of the archenteron , but they are not as 

 coarsely granular as the latter. Although in Actinotrocha^ Species, B., 

 the cells are found, in most cases, closely associated with the blood 

 corpuscles, I have never seen them in process of division and I do not 

 believe that they give rise to blood corpuscles. Their occurrence is 

 quite variable but so far as I have observed, they are not present in 

 the Actinotrochae which are ready to metamorphose. They are not 

 phagocytes nor are they pigment cells and the only name which I feel 

 justified in giving them is large free mesoderm cells. Frequently they 

 are also found in the posterior end of the trunk-cavity. 



In Actinotrocha., Species, B., the blood corpuscle-masses are four 

 in number; one pair in the same region as those of Species, A.., and the 

 other, in the anterior dorso-lateral part of the collar-cavity. All that I 

 am able to say concerning the origin of the blood corpuscles in this 



9 Arch, de Biol. Vol. 18. 1902. 



