126 FERNANDUS PAYNE. 



chromosomes, three of which are much smaller than the others, 

 and prove to be the univalent differential chromosomes. Here 

 they lie on the periphery. All the chromosomes divide equally 

 as the same total number (15) is found in the metaphase plate 

 of the second division. Now, however, the arrangement is dif- 

 ferent, the 12 larger chromosomes forming an irregular ring 

 within which lie the three differential chromosomes in the form 

 of a triad group, similar in arrangement to the pentad group in 

 Gelastocoris (Galguhts}. Two of these three, nearly or quite 

 of the same size, lie in the same plane, while the third, which is 

 a little larger, lies either above or below them on the other side 

 of the equatorial plane (Fig. 2, / and /, two side views of the 

 second division, metaphase). While my material does not show 

 the anaphases of this division, the relations in the male and 

 female cells and a comparison between this and the other two 

 species, which show the same type of distribution and where 

 anaphases are present, leave little doubt as to the manner of 

 division. The 12 chromosomes in the ring divide equally, while 

 the members of the triad group do not divide individually, but 

 the group as a whole separates so that the two chromosomes 

 pass to one pole and the one to the other. Two classes of 

 spermatozoa containing respectively 13 and 14 chromosomes are 

 thus produced. Since the female number is 28 and the male 

 27, it is evident that the reduced number in the egg must be 14, 

 and that females are produced upon fertilization of the egg by 

 the 14-chromosome class ; males upon fertilization by the 

 13-chromosome class, as follows: 



Egg 14 plus spermatozoon 13== 27 (J 1 ), 

 Egg 14 plus spermatozoon 14^ = 28 (?). 



Although the end result is the same as in those species with an 

 odd chromosome, this gives us a new type of chromosome dis- 

 tribution, which is the first step in a series, which bridges the gap 

 between the relations found in Diplocodus, on the one hand, and 

 Gelastocoris (Galgulus} on the other. 



The history of the differential chromosomes in the growth 

 period has not been followed in detail, but during the greater 

 part of this time, a pale plasmosome is present and embedded 



