Chromosomes m Germ-Cells of Culex 209 



the broken wall of the testis. The two testes are situated one 

 on each side of the digestive tract in the third segment from the 

 end of the tail of the pupa. Maturation occurs mainly, if not 

 wholly, during the pupa stage. 



Fig. 6 is a good specimen of an early prophase of spermatogonial 

 mitosis, showing three long granular chromatin threads, one of 

 which already shows its double character. Fig. 7 is a section of a 

 nucleus showing the twisted chromosomes of a later prophase 

 stage. Fig. 8 is a spermatogonium in metaphase, showing the 

 pairs separated and apparently all equal; Fig. 9 the chromosomes 

 from a similar stage, in outline, so as to show the full length of 

 each chromosome; and Fig. 10 a late prophase from a Flemming- 

 iron-haematox\lin section. In no one of these figures would one 

 suspect that one pair of chromosomes might be unequal, but in 

 the testes ot two individuals I found seven plates of a different 

 character, one of which is shown in Fig. 11, with the shorter pair 

 of chromosomes apparently composite, each consisting of a longer 

 and a shorter portion, the longer components equal, and the 

 shorter unequal and suggesting a case of unequal heterochromo- 

 somes such as occur in the Muscidae ('08). Had I not found these 

 cases, six in one testis and one in another, I should have said that 

 there was no evidence in the mosquitoes of any such hetero- 

 chromosomes as occur in so many other insects, and are clearly 

 present in the nearly related Muscidae. 



A very distinct synizesis stage occurs in which the granular 

 and beaded chromatin threads are wound about a large nucleolus, 

 which in Flemming material stained with thionin, is yellowish in 

 early stages and gradually acquires a staining quality nearly 

 equal to that of the chromosomes. Figs. 12, 13 and 14 were taken 

 from the same section to show an early synizesis stage with a 

 pale plasmosome, a later stage with blue-staining plasmosome, 

 and a pale spireme stage with the plasmosome stained a deep blue 

 (Fig. 14). This series suggests an extrusion of chromatin sub- 

 stance from the spireme during the synizesis stage and an absorb- 

 tion of the extruded material by the plasmosome. In Culex it 

 is quite certain that parasynapsis occurs in each cell generation 



