86 Edmund B. Wilson 



I have not succeeded with Pyrrochoris (as I have with several 

 other genera) in obtaining photographs of both anaphase daughter 

 groups showing all the chromosomes; but it is perfectly evident 

 that all divide equally in the first division, and all but the idio- 

 chromosome in the second. This chromosome lags behind the 

 others and then passes undivided to one pole where it is included 

 in the daughter nucleus (Photos 47 to 49) as Henking described. 

 This pole thus receives twelve chromosomes, the other but eleven. 

 As in a number of other species the idiochromosome retains its 

 compact form and deep-staining capacity long after the reconstruc- 

 tion of the nuclei and the breaking up of the other chromosomes. 

 It may thus be distinguished (especially well in safranin prepara- 

 tions) up to a rather late period stage of the spermatids, even after 

 the tails have grown out. It finally disappears from view, and the 

 mature spermatozoa show no visible indication of their dimorphism. 



GENERAL 



If my conclusions are correct, Pyrrochoris agrees exactly with 

 other forms in which an unpaired idiochromosome is present. 

 Syromastes however presents a new type in which the "accessory" 

 chromosome is not univalent but bivalent, and in which accord- 

 ingly half the spermatozoa receive two more chromosomes than 

 the other half. If we may apply the same rule to Syromastes as 

 that which holds for other Hemiptera we may expect the sperma- 

 tozoa that receive the "accessory" to be female-producing, the 

 others male-producing. The fertilization formulas for the two 

 species considered in this paper should therefore be as follows : 



PYRROCHORIS 



Egg 12 + spermatozoon ii = zyote 23 (d') 

 Egg 12 + spermatozoon 12 = zygote24(9) 



SYROMASTES 



Egg 12 (including 7 and ;')* + spermatozoon 10 = zygote 22 (including/ and /)(c?) 



Egg 12 (including /and/') + spermatozoon 12 (including / and/) = zygote 24 (including 



* The formation of a reduced female group of this composition may readily be explained if it be sup- 

 posed that in synapsis the two small idiochromosomes couple with each other to form the bivalent 

 ;'/, the two large ones to form the bivalent II. 



