THE DETERMINATION OF SEX 



577 



for a knowledge of which we are indebted mainly to Payne. 1 

 In Fitchia and Thyanta X is double, in Prionidus and Sinea it is 

 triple, and in Gelastocoris quadruple, forming with the Y-chromo- 

 some in these respective cases triad, tetrad, or pentad elements 

 (fig. 2; fig. i,g). In every case the compound element behaves 

 in maturation like a single XY pair, the single Y-chromosome 

 passing to one pole and the compound X-element to the other. 

 All these cases are evidently reducible to the same fundamental 

 type. The X-chromosomes, though separate in the diploid 

 groups, behave in maturation like a single element and always 

 pass together to one pole. It is a plausible view, advanced 



Different tied/ 



Division 

 in, the Male 



Afatu.ra.tion 



Dty is ion- 

 en t/t/e Female 



Afe-zara 



Oncopeltus 



Lygacus 

 Eiischistus 



Prote/ior 

 Pyrrhocoris 



9 

 A • 



9 

 



: 



Syrvmasfcj 

 Phylloxera 



Fitcfiia 



Thytintfi 



Sine^a. 

 Priori iclu^ 



9 ffi 9 

 oU»0 



Y class 

 JSr class 



7\rclass 

 r\.-ctass 



Diploid 

 Afticle,i 

 (Male) 



Sperm Y 

 Egg X 



Diploid 

 Nuclei 



(Female) 



Sperm X 

 Egg X 



Fig. 2. — Diagrams of different types of the chromosome-relations in the Hemiptera. 



None of the figures show either the exact number or size-relations of the chromosomes. In all cases the 

 ordinary chromosomes are in outline, the X-chromosomes in black, and the Y-chromosome with cross 

 bar. The maturation-divisions in the females of the types illustrated have actually been worked out 

 only in Protawr (Morrill). 



by Payne, that the compound X-element in these cases was 

 originally a single chromosome (large idiochromosome) which 

 has secondarily become divided into a number of components. 



(II) The foregoing are the most essential facts regarding the 

 dimorphism of the spermatozoa. What, now, is the evidence 

 that this dimorphism is connected with sex-production? Im- 

 mediate ocular evidence of the fact has not yet been obtained ; 

 for no one has yet been able to trace completely the history of 

 the two kinds of spermatozoa in the fertilisation of the insect 

 egg. Nevertheless, that the two kinds must be respectively 



1 Biol. Bull. 1909, xvi. 



37 



