ON MONOPYLEPHORUS LIMOSUS. 37 



face of septum X/XI in the same longitudinal line with the testes. 



6). Ovisac. This is a posteriorly directed outgrowth of septum 

 XI/XII and lies on the dorsal side of the intestine, sometimes 

 reaching to segment XIX. 



As to the sexual maturation of the worm the testes and the 

 sperm-sacs first attain full development, the latter being filled with 

 sperm- cells which are going through the developmental changes ; 

 the ovaries are in this stage not yet ripe and no ova are to be seen 

 in the ovisac, its thin wall closely adhering throughout to that of 

 the posterior sperm-sac. Subsequently the ovaries ripen and some 

 young ova are seen floating in the cœlom. In this stage a few 

 ova may sometimes be found at the bottom of the ovisac, closely 

 invested by the walls of the ovisac and the posterior sperm- sac, 

 but they are young and contain no yolk granules or only a small 

 number of them. When many riper ova are found in the ovisac, 

 the posterior sperm-sac gradually decreases in length while the ovisac 

 attains its full size, and cell multiplication ceases in the testes, which 

 nearly disappear, the sperm-cells having mostly changed into 

 spermatozoa. 



7). Oviducts. In spite of my utmost efforts, I have not been 

 able to find them out. I may however state that in the oldest 

 specimen accessible to me, there was in the furrow of the inter- 

 segment XI/XII (clitellum) on the ventral median line of the body 

 a small patch of ordinary hypodermis, which seems to me to indicate 

 the future female pore. 



3. Comparison 



of Monopylephorus limosus and other species of the genus. 



For comparison I reproduce the main points of systematic 

 importance from the descriptions of the known species of this 

 genus, mostly in the words of the respective authors. 



