On the Development of the Sexual Organs and 

 of Their Products in Phoronis. 



BY 



Iwaji Ikeda, Bigahishi. 



With Plate V. 



In Phoronis ijimai and P. australi*, as in all other species of the 

 genus, the ovary and testis are situated in the posterior part of the body, 

 on one side of the stomach. When fully developed, they represent two 

 elongate and loose masses of 1-2 mm. in length, lying side by side— the 

 ovary dorsally to the testis — in close apposition with each other and 

 nearly filling up a lateral chamber of the body-cavity in the region 

 indicated. Clasped between the two organs runs the efferent blood- 

 vessel. This sends forth numerous, branched or simple, blindly ter- 

 minating capillaries, which may be distinguished into two series, the 

 ovarian and the testicular, according to the organ they penetrate into. 

 Of great importance are these capillaries in the genesis of the sexual 

 glands, as giving the fundament for their development. 



In young individuals — say, in all those which have not yet attained 

 the full adult size— the sexual grands are without a trace. In their stead 

 there exist only the said capillaries, the so-called cœcal or contractile 

 capillaries, which, arising as slender thin-walled off-shoots from the 

 efferent od-vessel, lie free in the body-cavity. The capillary wall 

 consists of three layers, i.e., (1) the endothelium, (2) the peritoneum and 

 (3 the connective-tissue layer lying between the above two. Of these 

 thiee ^yers the middle one is tl at which in the larger vessels bears the 



