288 ELIZABETH A. SMITH. 



In the formation of the tetrad, they found that the long axis 

 of the tetrad is identical with the long axis of the chromatin 

 threads of the growth period, and the first maturation division 

 would separate univalent chromosomes and be a reducing divi- 

 sion if the conjugation took place end to end. To quote the 

 rest of the conclusion, "If, however, it should prove true of this 

 form that a parallel conjugation occurs, as has been suggested, 

 the first division would still be a reducing one, since the axis of 

 the crosses are not reversed by the drawing out of the transverse 

 arms and the attachment to the spindle fibers is at the end of the 

 longitudinal arms." 



Zeleny and Faust ('15) in the figures of Lefevre and McGill 

 ('08) have measured the chromosomes and calculated a bimodal 

 curve for the two classes of spermatozoa which must result 

 from the behavior of the odd chromosome. 'These give ex- 

 pected ratios of i.oo : 1.07 on the basis of complete fusion of 

 chromosomes and production of spermatozoa of like shape and 

 i.oo : 1.09 for end to end fusion of chromosomes." The sperma- 

 tozoa of Mschna canadensis in which the chromosomal content is 

 unknown give a bimodal but unequal curve. 'The two modes 

 are at 50.2 ju and 51.6/1, giving a ratio of I.oo : 1.03. This is 

 considerably less than the ratio i.oo : 1.07 or i.oo : 1.09 that 

 would be expected for Anax jitnius" 



VII. GENERAL CONSIDERATIONS. 



In Anax, Sympetrum and Libellula, the spermatogonial chromo- 

 somes are 27, 25, and 25 respectively. Throughout the growth 

 period, a condensed chromatin body persists which from its 

 subsequent behavior can be identified as the sex-chromosome. 

 In the spermatocyte, a synapsis occurs and the autosomes form 

 quadripartite bodies, all of which are bivalent. In the first 

 division in Anax and Sympetrum the bivalents and the sex- 

 chromosomes divide, and this division as far as the former are 

 concerned probably represents a pulling apart of the univalent 

 chromosomes which conjugated in synapsis and is therefore a 

 true reduction division. Upon this assumption, the second 

 division which splits the univalents must be equational. The 

 sex-chromosome undivided goes over to one pole in the second 



