36 Cutler, fart/ienogenesis in Animals 



usually undergone reduction before they are treated, and on the 

 theory of sex chromosomes the majority of eggs with one X 

 chromosome would develop into males. In those animals which 

 are heterozygous for sex in the female two> kinds of eggs would 

 be formed and males and females would be expected to hatch 

 from the eggs. Unfortunately, the facts are very few. Delarge 

 obtained one sea urchin which he was able definitely to> state to 

 be a male, while Loeb and Bancroft reared two> young frogs 

 which they thought to be females. Recently Gatenby had pub- 

 lished a short account of the se(x> of a frog raised by artificial 

 parthenogenesis, and he is sure 'that it was a male. He also 

 mentions in the paper that Loeb has announced to an American 

 conference that an American species of frog produced by arti- 

 ficial parthenogenesis had proved to be a male. 



A second question which is still uncertain is whether the hap- 

 loid number of chromosomes is retained during the development 

 of artificial parthenogenetic eggs. Wilson states that the reduced 

 number is maintained in the sea urchin, but Delarge asserts that 

 the normal number (Diploid) is restored by an auto-regulation. 

 Handle was able to count the number of chromosomes in the 

 cells up to the blastula stagej in Strongylocentrotus purpuratus 

 and found the reduced number throughout. 



It is stated above that artificial parthenogenetic eggs have 

 usually undergone maturation before treatment, but a few ex- 

 periments have been made on the result of treating eggs which 

 have not formed the polar bodies. Delarge used the eggs of 

 Asterias glacialis and found that he got the best results with eggs 

 that had not formed the polar bodies. From this he concluded 

 that the retention of chromatin was an important factor. Gar- 

 bo wski, however, with the same species of egg obtained results 

 entirely different from those of Delarge. Finally Morris, who 

 induced artificial parthenogenesis in Cumingia eggs by subject- 

 ing them to heat, found that normal blastulas were developed 

 from those eggs which had not produced their polar bodies. 



These results are of interest in connection with the work of 

 Kostanecki on Mactra, the only member of the Mollusca in which 

 natural parthenogenesis has been studied. Here the eggs may 

 develop and entirely omit maturation. It is premature to draw 

 any parallel between the polar body formation in natural par- 

 thenogenesis and artificial, but there is evidence, I think, to 

 warrant the belief that in the future some important connection 

 may be discovered. 



Meanwhile the problems of fertilisation is still far from 

 settled. Loeb sees the chief value of the experiments in that 



