CHROMOSOMES OF MOSQUITO 525 



11. OBSERVATIONS 

 A. SPERMATOGENESIS 



a. Introductory 



The testes of Culex pipiens are two ellipsoidal, colorless, 

 highly refractive bodies lying laterally in the sixth, abdominal 

 segment. Each consists of a single follicle, divided by partitions 

 of connective tissue into a number of cysts. The spermatogonia 

 are formed in the cephalic end and these are followed by the 

 successive stages of spermatogenesis as shown in text figure 1, 

 which is from a longitudinal section of a pupal testis at a magni- 

 fication of 1800 diameters. The numbers to the right of the 

 figure refer to the successive stages as illustrated by figures 1 

 to 93. Usually not all stages will be found in a single testis, 

 but I have occasionally found an individual with divisions of 

 spermatogonia, first and second spermatocytes, and with sper- 

 matids. The development of the germ cells is not completely 

 correlated with the age of the insect, but considerable variation 

 obtains. 



b. Spermatogonia 



The last spermatogonial division and the 'resting' nuclei pre- 

 ceding it are the earliest stages found in full grown larvae and 

 pupae. Probably younger larvae would show a greater number 

 of spermatogonial generations. 



1. Prophases. The earliest stage obtained is illustrated by 

 figures 1 and 2. The chromosomes are very thin and only partly 

 visible. A large irregular, diffuse nucleolus is a striking charac- 

 teristic of this stage. If often shows four darker areas (fig. 1). 

 There may be more than one nucleolus (fig. 2), together equiva- 

 lent, however, in size and staining qualities to the one. The 

 nucleolar elements are clearly attached to the chromatic threads, 

 which may sometimes be traced to the periphery of the nucleus. 

 They show no tendency to be approximated to the side of the 

 nucleus, but occupy various positions in the karyolymph. 



JOURNAL OF MORPHOLOGY, VOL. 28, NO. 2 



