286 ELIZABETH A. SMITH. 



are present; one containing 12 chromosomes and the other 13 

 chromosomes. Figs. 114, 115, 116, are polar views of secondary 

 spermatocytes. Fig. 116 shows two cells formed from one 

 primary spermatocyte lying side by side, and in one there are 

 13 chromosomes and in the other 12. In one cell the sex-chromo- 

 some seemed to pass undivided to one pole as shown in Fig. 117 

 and in Fig. 118 it remains undivided at the metaphase. Figs. 

 119 and 1 20 represent secondary spermatocyte spindles while 

 in Figs. 121 and 122 the dividing sex-chromosome stands out 

 distinctly from the autosomes. Fig. 123 is a telophase stage. 



After the second maturation division the chromosomes become 

 fused into several large masses connected by a reticulum as in 

 Sympetrum. The irregularity of the grouping leads to the con- 

 clusion that the number of masses has nothing to do with the 

 presence or absence of the sex-chromosome and the difference 

 in the amount of chromatin is not noticeable in the spermatids. 

 The cytoplasm around the nucleus elongates and the centrosome 

 is found near the largest mass of chromatin. The axial filament 

 grows out from the centrosome which increases in size until it 

 forms a knob. This is the only thing comparable to a middle- 

 piece, and as the nucleus elongates it becomes so closely asso- 

 ciated with the large chromatin mass that it can no longer be 

 distinguished from it. Figs. 124 to 128 inclusive are drawn 

 from living material. The spermatozoon moved with a pecu- 

 liarly spiral motion such as that described for Sympetrum. In 

 Fig. 127 the cytoplasm is spread out at the base of the head, 

 probably an abnormal condition. The spermatozoon did not 

 move rapidly but progressed continuously. In the mature 

 spermatozoon no head-spine was visible upon the rod-like head 

 which comprises about one third of the length of the whole 

 spermatozoon. 



VI. HISTORICAL REVIEW. 



There has been little work done upon the cytology of the 

 Odonata. Of historical interest only are the papers by C. Th. 

 von Siebold (1840) and Biitschli in 1871. Von Siebold deals 

 mostly with the mating habits of the Libellulidae, though he 

 made some observations upon the spermatozoa. According to 

 his account, the spermatozoa have in general the characteristic 



