56 A. FRANKLIN SHULL. 



in different eggs. If such differences existed, they might repre- 

 sent the two types of female. The possibility that Lenssen 

 believed the number of chromosomes to be different in different 

 individuals is heightened by his statement that the reduced 

 number in the egg of the male-producer is "probably five." 

 This would suggest 10 as the diploid number in the male- 

 producer, though maturation phenomena might reduce the 

 haploid number to less than half the diploid. 



Whitney's ('09) studies threw no light on Lenssen's state- 

 ments, for he was unable to count the chromosomes with 

 accuracy. Using American specimens, he arrived at a diploid 

 number between 20 and 30, the highest number actually counted 

 being 25. There was nothing in the male egg or fertilized egg 

 to render the count more definite, for the number discovered 

 in the male egg ranged from 10 to 14, and in the fertilized egg, 

 during maturation, 14 was the largest number seen. 



In view of the uncertainty of these determinations, and of the 

 possibility that the male-producing and female-producing females 

 might differ in their chromosome number, I undertook a re- 

 examination of this difficult material. Notwithstanding the 

 difficulties, I have a fair degree of confidence in the conclusion 

 reached. 



PREPARATION OF MATERIAL. 



Although several fixing agents were used, the specimens that 

 were good enough to study were all fixed in Bouin's fluid. De- 

 hydration was accomplished by the drop method. When the 

 objects had reached 70 per cent, alcohol, they were carefully 

 wrapped in bits of stratum corneum of frog skin, which had 

 shortly before been put into 70 per cent, alcohol, in order to make 

 the objects large enough to imbed easily. The frog skin was 

 held in compact form by fragments of cover glass until the 

 objects were in 96 per cent, alcohol, by which time the skin had 

 hardened so that it would not unroll. Six to eight rotifers were 

 as a rule wrapped in each roll. Sections were all cut 5 n in 

 thickness. All were stained in iron-hematoxylin. They were 

 also lightly stained with eosin, but not for the purpose of this 

 study. Unfortunately the chromosomes show a strong tendency 



