SPERMATOGENESIS OF THE DRAGON-FLY. 289 



division. In Libellula, upon assuming parasynapsis, the first 

 division represents a true reduction in every way for the bivalents 

 divide and the sex-chromosome goes to one pole undivided. 

 Certain stages enumerated in the description of Sympetrum 

 differ from what Lefevre and McGill described for Anax. 



VIII. SUMMARY. 



1. The maturing sex-cells are arranged in cysts in the testes, 

 but there is no definite seriation as to age like that found in 

 many insects and vertebrates. 



2. The spermatogonial chromosomes are twenty-five in number 

 and are closely crowded together, making it impossible to tell 

 much about their behavior. 



3. The evidence obtained seems to indicate that the leptotene 

 threads unite side by side (parasynapsis) to form a spireme 

 which is twisted in such a way that the loops are oriented toward 

 one side of the nucleus. 



4. This spireme breaks up into segments which open out pre- 

 sumably along the original axis of synapsis to form rings. These 

 condense into crosses and then into quadripartite bodies or 

 prophase chromosomes. 



5. The primary spermatocyte contains 12 bivalent autosomes 

 and one sex-chromosome. The bivalents divide apparently 

 along the line of their original junction making this the reduction 

 division for them while the sex-chromosome divides equationally. 



6. In the second spermatocyte division all the univalerit 

 autosomes divide equally while the sex-chromosome passes to 

 one pole undivided; thus two kinds of spermatids are formed. 

 These change into linear spermatozoa which show no visible 

 difference. But the one which possesses the sex chromosome 

 must be physiologically different. 



7. In Libellula basalis the spermatogonial number is 25; the 

 reduced number, 13, consists of 12 bivalent autosomes and I uni- 

 valent sex-chromosome. The sex-chromosome, unlike its pro- 

 cedure in Sympetrum, passes undivided to one pole in the primary 

 spermatocyte division, forming two kinds of secondary spermato- 

 cytes. In the secondary division the sex-chromosome divides 

 equally. Two kinds of spermatozoa are thus formed which 

 must have a functional difference. 



