10 SEX-DETERMINATION 



the number of X-chromosomes within the group, the group 

 itself is single in one sex, double in the other, so that 

 essentially this difference is of the XOrXX type or, as is 

 sometimes the case, XY:XX, for the single compound X is 

 in certain species associated with a Y-chromosome. Ray- 

 Chaudhuri and Manna (1950) report that the male of the 

 gryllid Euscyrtus is X^X^Y. The Y can itself be compound. 

 Thus in the dioecious plant Rumex acetosa Kihara and Ono 

 (1923) found a Y-chromosome consisting of two elements 

 in association with a single X. According to Sharman, 

 Mcintosh and Barber (1950) the rat kangaroo is XY^Y^ in 

 the male, XX in the female. 



The first account of a sex-chromosome difference was that 

 of Henking (1891), who described in the bug Pyrrhocoris 

 apterus a peculiar chromatin element which was condensed 

 in the early prophase of the primary spermatocyte. In the 

 first spermatocyte division the twelve elements found in the 

 metaphase plate all divided equally, but in the second divi- 

 sion one of the twelve elements lagged and finally passed 

 undivided into one of the two daughter cells. As a result two 

 kinds of spermatids were formed, one with eleven and one 

 with twelve of these elements. Henking did not at this time 

 refer to this odd chromatin element as a chromosome but 

 called it a 'nucleolus'. He did not confuse it with a true 

 nucleolus, however. 



In 1898 Paulmier recorded a similar phenomenon in 

 Anasa tristis, in the second spermatocyte division of which 

 eleven chromosomes passed to one pole and ten to the other. 

 In 1 90 1 de Sinety described the behaviour of what he called 

 a 'chromosome special' in the male of Orphania. In the 

 same year McClung suggested that the two classes of 

 spermatozoa resulting from the meiotic distribution of the 

 'accessory' chromosome must be causally related to the 

 production of the two sexes. 'Upon the assumption that 

 there is a qualitative difference between the various chromo- 

 somes of the nucleus it would necessarily follow that there 

 are formed two kinds of spermatozoa which, by fertilization 

 of the egg, would produce individuals qualitatively different. 

 Since the number of each of these varieties of spermatozoa 



