1 6 Cutler, Parthenogenesis in Animals 



eggs and give rise to sexual fe m ales and males, which constitute 

 the Summer brood. The Spring generation is also peculiar in 

 that two kinds of females are nroduced. from the one kind, eess 

 are laid from which only males develop, from the other type 

 only sexual females. 



The somatic number of chromosomes is twenty in both the 

 Spring and Summer generations. One of the points of interest 

 is that the two types of females of the Spring" brood differ in 

 regard to the method of maturation of the eggs. 



In the female-producing eggs no maturation divisions occur, 

 and the chromosome number is not reduced, thus there are 



twenty chromosomes in the female pronucleus. 



In the male-producing eggs, however, two maturation divisions 

 take place and the chromosomes are reduced to ten. 



Here then we have a condition which parallels wha: occurs 

 in the formation of the drone bee. 



Spermatogenesis is also similar to that of the bee. The sper- 

 matogonia contain ten chromosomes but :here is no reduction of 

 chromosomes. The nrsr division gives rise, as in the bee, to an 

 enucleate bud of protoplasm, and a functional spermatocyte with 

 ten chromosomes. At the second maturation the chromosomes 

 divide and there are formed two spermatids, each with ten 

 chromosomes. 



During oogenesis two maturation divisions take place, one 

 of them reductive: in this way four groups of chromosomes are 

 formed, of which the three outer form polar nuclei and the 

 innermost, with ten chromosomes, the female pronucleus. The 

 accompanying scheme illustrates the essential phases of the life 

 history. (Diagram T 



A point which still remains doubtful is what determines 

 whether the Spring lemales shall be male-producing or female- 

 producing. This was the subject of an investigation which 

 Doncaster and I undertook. It was hoped that it might be 

 possible to show that there were two classes of spermotozoa 

 formed, but this expectation was not realised. At present it is 

 impossible to indicate with certainty what constitutes the differ- 

 ence between these two classes of parthenogenetic females. 



Rhodites rosce. — Males are very rare in this species. In 

 fact Schliep. a recent worker, found none during the course 

 of his experiments: on rare occasions, however, they are said to 



; ::_r 



He n kin g 1S92; stated that the somatic number of chromo- 

 somes was eighteen, which were reduced to nine in the eggs 

 before maturation. The maturation division of the eggs was 



