382 L. DONOASTEB. 



minent nuclei;, and at this stage also there is no vestige of 

 genital ducts, either male or female. The period in which 

 this condition lasts seems to vary in different species ; in 

 small species, such as S. minima, very small specimens are 

 found further advanced ; while in the larger ones, e. g. 

 S. lyra, I have found individuals more than two centimetres 

 long with the genital rudiments in this condition, and with 

 no trace of ducts visible either alive or in sections. 



As the further development of the male organs differs 

 greatly from that of the female, it will be convenient to deal 

 with them separately, and since the male portion of the 

 animal is the first to become mature, that will be described 

 first. 



Grassi (4) has described the adult generative organs with 

 great detail and accuracy, and made a study of the spermato- 

 genesis ; he points out how when the testis reaches a certain 

 size it gives off into the tail-coelom groups of " sperm- 

 cumuli," which there com})lete their development, and men- 

 tions the fact that the coelom of the tail becomes divided by 

 secondary septa, the position of which in the large species 

 differs from that of the smaller. He also describes and 

 figures the structure of the vasa deferentia and vesiculee 

 seminales of the adult, and it is therefore not necessary here 

 to go over these points. As the animal develops, the group 

 o£ cells mentioned above, which represents the testis, 

 increases in size and grows backward along the body-wall, 

 and at the same time projects somewhat into the cavity, 

 Vjecoming cylindrical in shape instead of lenticulai'. 



In S. bipunctata at this stage the secondary longitudinal 

 septa arise, one on each side, dividing each half of the tail 

 cavity into two compartments ; but since they occur only in 

 the middle region, and die out both in front and behind, the 

 cavity remains continuous at each end. The septa are 

 exceedingly slender, and contain here and there faintly 

 staining nuclei ; I have not been able to discover their mode 

 of origin. When the testis has increased considerably in 

 size it begins to give off masses of cells which fall into the 



