Il6 N. M. STEVENS. 



stages. The pupae were thought to be Anopheles but no larvae or 

 adults were secured for identification. It was supposed that the 

 few specimens obtained must have wintered over, probably in 



36 



38 



FIG. 35. Anopheles sp.? First spermatocyte growth stage. X = the hetero- 

 chromosome. 



FIG. 36. First spermatocyte prophase. 



FIGS. 37 and 38. Chromosomes of the first spermatocyte metaphase. Mag. 

 2,000 in all figures. 



the larval stage. The net was used in the pond many times during 

 March, April and May, but no mosquito larvae or pupae secured 

 except on the two dates given above. 



Fig. 35 shows the heterochromosome in the nucleus of a growth 

 stage, Fig. 36 a prophase of the first maturation mitosis, and Figs. 

 37 and 38 the six chromosomes from two first spermatocyte 

 spindles. The largest pair is slightly unequal but not composite 

 as in Anopheles punctipennis. 



DISCUSSION. 



As we have already seen, the various species of Culicidae, thus 

 far studied, present peculiarities not hitherto encountered in the 

 study of heterochromosomes in the various groups of insects. 



In Anisoloba maritima (Randolph, '08) and several species 

 of Lepidoptera (Stevens, '06; Dederer, '07; Cook, '10) there 

 is an equal pair of heterochromosomes distinguishable as such by 

 their condensed condition in the growth stages of the first 

 spermatocytes. In Drosophila ampelophila the unequal pair of 

 heterochromosomes of the maturation mitoses is not condensed 



