On the reproductive system of Planaria simplissima. 461 



Conclusion. 



The important feature of the reproductive system in Planaria 

 simplissima is its almost diagrammatic simplicity. This is due to the 

 small number of testes and testicular canals and the absence of accessory 

 organs or glands other than the vaginal shell glands, in the region of 

 the atrium and uterus. Because of the small number of testes the 

 testicular canals are especially well shown. The small number of 

 testes would make a metameric condition very evident, but an ex- 

 amination of many specimens shows that the arrangement is entirely 

 irregular. 



The ovaries are not compact, but composed of straggling lobes 

 and portions are often found at a considerable distance behind the 

 ovary having no apparent connection. One is struck by the close 

 resemblance between such lobes and the branches of the yolk glands 

 leading from the oviduct at its upper end. As the ova grow there 

 appear in the cytoplasm an increasing number of what seem to be 

 vacuoles containing globules of varying density or irregular shaped 

 masses. Smaller vacuoles are sometimes found in the yolk-cells. 



The uterus is a slightly curved tube of uniform diameter with 

 no terminal enlargement. The arrangement of the common oviduct, 

 uterus and vagina is such that the ova coming out of the oviduct could 

 easily enter the uterus. The fact that spermatozoa were never found 

 there but always found along the oviduct or collected at its head 

 close against the ovary makes it unlikely that fertilization can occur 

 in the uterus. 



On the activity of the germinal elements from October to April 

 only negative results were obtained. The condition throughout the 

 period has been one of slow production of spermatozoa which make 

 their way to the seminal vesicles as soon as mature and slow 

 growth of the individual ova with no apparent increase in number. 



With reference to other structures there were noted in the fibres 

 of the main longitudinal system certain dark areas. These lie 

 in the "Rindenschicht" of the fibre and possibly represent nuclear 

 material. 



I wish to acknowledge the assistance in matters of technique 

 which was rendered me during the summer of 1898 by the late 

 Dr. Arnold Graf, who was then connected with the Marine Biological 

 Laboratory at Woods Holl Mass, • 



