FUNCTIONAL AND RUDIMENTARY SPERMATOZOA 333 



cells degenerate and a certain percentage of the sperm cells 

 develop normally, thus giving a definite ratio of degenerate and 

 normal sperm cells. In the phylloxerans this ratio has not been 

 determined but in the rotifers there is one degenerate sperm cell 

 to two normal sperm cells. As all the fertilized eggs in both 

 phylloxerans and rotifers develop into female young it seems 

 safe to conclude, as Morgan has already concluded, that the de- 

 generate sperm cells are the male-determining ones and that the 

 normal sperm cells are the female-determining ones. 



SUMMARY. 



1. The normal and motile spermatozoa of Brachionus mulleri, 

 Brachionus amphiceros, Hydatina senta and Diaschiza sterea 

 possess large heads in which is located the chromatin material. 



2. The motile bodies of seven other species of rotifers which 

 were figured and considered as the normal spermatozoa in the 

 former paper were probably only the tails of such normal sper- 

 matozoa. 



3. The degenerate and immotile spermatozoa as seen in 

 Brachionus mulleri and Hydatina senta also possess heads in 

 which there is chromatin material. 



4. The stiff processes, called rudimentary spermatozoa in the 

 former paper, are now considered to be not the complete rudi- 

 mentary spermatozoa but only the degenerate tails of these 

 rudimentary spermatozoa. 



5. The sperm head in the fertilized egg of Hydatina senta is 

 about the same size as the head of the normal spermatozoon of 

 this species. 



6. The four species of rotifers enumerated above together 

 with the seven other species described in the former paper con- 

 stitute eleven species of rotifers in which both normal and rudi- 

 mentary spermatozoa have been found to occur. 



ZOOLOGICAL LABORATORIES, 



THE UNIVERSITY OF NEBRASKA, 



LINCOLN, NEBRASKA, January 5, 1918. 



LITERATURE. 

 Federly, H. 



'13 Das Verhalten der Chromosomen bei der Spermatogenese der Schmeller- 

 lenge, etc. Zeit. f. unduktive Abstam. Vererb., Bd. 9. 



