284 ELIZABETH A. SMITH. 



V. SOME NOTES ON LIBELLULA BASALIS. 



The chromosomes of Libellula basalis in a general way undergo 

 the same changes described for Sympetrum. The cells are 

 larger; the diploid number of chromosomes is twenty-five, the 

 reduced number thirteen. From the fact that certain cysts 

 contain as few as eight large spermatogonia, while others contain 

 large numbers of smaller ones, it is evident that several spermato- 

 gonial divisions occur. In several cysts in which an attempt 

 was made to count the later spermatogonia, from 45 to 100 were 

 present. The nucleus of a spermatogonium is usually eccen- 

 trically placed in the cell and part of the chromatin forms a 

 large irregular nucleolus which is connected with chromatin 

 nodules around the periphery of the nucleus by a few faintly 

 staining threads. Fig. 80 shows such a cell from an aceto- 

 carmine preparation, while Fig. 81 represents another from 

 a section stained in iron-alum hematoxylin ; Fig. 82 is a spermato- 

 gonium drawn under low power and is of interest since it was 

 taken from a living cell in salt solution. In all the cells examined 

 in this way, the protoplasm was drawn out into projections which 

 resembled pseudopodia though no actual movement was ob- 

 served. 



In the prophase of the last spermatogonial division the chromo- 

 somes appear as the rod-like bodies shown in Fig. 83. In polar 

 views 25 chromosomes can be distinguished, but the sex-chromo- 

 some cannot yet be singled out. Figs. 84 and 85 depict spermato- 

 gonial polar views. Figs. 86 to 90 inclusive picture various 

 stages of the last spermatogonial division. Fig. 91 shows how 

 the chromatin forms masses, each of which in turn makes a 

 leptotene thread. 



No detailed study of the growth period was made and conse- 

 quently the nature of synapsis cannot be set forth. However, 

 in the aceto-carmine smears made for hasty observations, the 

 spireme was much plainer than in the sectioned material and in 

 several cells, all the loops could be followed proving that the 

 spireme was more or less continuous. In one cell in particular 

 the spireme was composed of two parallel threads which were 

 looped and twisted side by side. Figs. 92, 93, and 94 are repro- 

 ductions from the aceto-carmine smears. Fig. 95 is a drawing 



