8 Cutler, Parthenogetiesis in Animals 



Sperms of the second type fertilising an ovum will produce 

 males, while those of the first type will form females. 



In passing, it is worth mentioning that from the inheritance of 

 sex limited characters there is reason to think that 1 ' in a few 

 animals, Lepidoptera and Birds, the reverse is the case and the 

 female has two* kinds of eggs. Cytological investigation has 

 largely confirmed this view. 



In light of these facts it is of considerable importance to dis- 

 cover what occurs in the maturation of parthenogenetic eggs. 



The question as to whether the chromosomes are reduced in 

 number at the maturation divisions of the parthenogenetic egg 

 is full of interest, and, as will be seen, in those eggs in which 

 reduction does occur, modifications have developed to ensure that 

 the normal number is reformed in subsequent generations. 



Ostracoda and Cladocera. — The parthenogenetic eggs of the 

 Ostracoda have only one maturation division, which is equational, 

 so that the number of chromosomes is not reduced. 



Weissmann, in 1886, sho(Wed that the parthenogenetic eggs 

 of Polyphemus produced only a sjngle polar body and thatf: 

 the chromosome number was not altered. Kuhn investigated 

 the parthenogenetic eggs of Daphnia pulex and Polyphemus 

 pediculus and arrived at the 'same conclusions. The cytological 

 aspect of male production in these forms has not been in- 

 vestigated. 



Branchiopoda: — Von Brauer (1893) as a result of research 

 on Artemia sauna announced that there were two types of par- 

 thenogenesis occurring in the same animal. In the first and 

 most common the chromosome number was not reduced and 

 only one polar body was formed. In the second type, however, 

 both polar bodies were developed, and during the formation of 

 the second the chromosome number was halved. This second 

 polar body, however, instead of passing to the exterior of the 

 egg and degenerating remained in the egg and gave rise to a 

 reticular nucleus, which fused with the female pronucleus. Thus 

 there was fertilisation by the second polar body. 



Petrunkewitsch (1902) reinvestigate*! the subject, but was 

 unable to find any trace (of the second type of parthenogenesiis. 

 He therefore concluded that it twas; due to a pathological con- 

 dition and was not a natural o|ne. 1 Th^'s was in the main the 

 conclusion of Fries (1909). 



Finally, in 191 1 and 1912, two papers appeared by Artom in 

 which it was stated thajt there were two* races of Artemia, a 

 parthenogenetic one and a sexual. The former differs from the 

 latter in possessing a double number of chromosomes. The par- 

 thenogenetic race (Artemia bivalens) develops with the diploid 



