142 



I. IKEDA. 



character of a tolerably thickly (level >pel muscular layer. Both the 

 endothelium and the peritoneum are made up of th î usual flat cells. 

 Needless to say that all the layers are directly continuous with the 

 corresponding layers in the wall of the efferent blood-vessel. 



All the subsequent changes leading to the formation of the ovarian 

 or th ! testicular tissue concern only the peritoneal layer of the contractile 

 capillaries. It may here at once be mentioned that that layer has to 

 serve for a time as reserve ground for certain nutrient matter and is 

 then absorbed, becoming finally completely replaced by the sexual cells 

 of likewise peritoneal origin. The changes begin to take place after the 

 animal has attained neavly or quite its full size. Among the specimens 

 of P. ijimai obtained and preserved in the months of December to May 

 and of P. australi* killed in September, I have found some individuals 

 with the sexual organs already fully developed, while in others they were 

 still in an earlier or a later stage of development. 



As the prelude to the development of the sexual glands, a part of the 

 cells forming the peritoneal layer of the capillaries transforms itself into 

 a peculiarly characterised epithelial tissue, which has been called by 

 Kowalewsky the " Fettgewebe " and by Cori* the " Gefassperitoneal- 

 gewebe." That this tissue is derived from the originally flat peritoneum 

 of the capillaries has been correctly pointed out by Cori. The 

 peritoneal cells increase in number, although I have not been able 

 to see direct proofs of cell-division. At the same time the majority 

 of them, but not all, become bulky, growing more especially in 

 height, which is due in a measure to the accumulation of the yolk-like 

 inclosures soon to be noticed. This change, so far as I have seen, 

 begins at the basal part of the capillaries, that is to say, near 

 the junction of these with the efferent blood-vessel, and thence proceeds 

 distally towards their blind ends. The peritoneum of the efferent 

 vessel itself never participates in the above metamorphosis ; it is 

 seen to pass gradually and continuously into the now greatly thickened 

 and much altered peritoneal layer of the capillaries at the base of these. 



* Zeitschr. f. Wiss. Zool., Bd. 51, 1891. 



