SPERMATOGENESIS OF THE DRAGON-FLY SYMPE- 



TRUM SEMICINCTUM (SAY) WITH REMARKS 



UPON LIBELLULA BASALIS 



ELIZABETH A. SMITH, 

 DEPARTMENT OF ZOOLOGY, UNIVERSITY OF WISCONSIN. 



CONTENTS. 



Introduction ... 269 



I. Description of Nymphs 270 



II. Testes . 270 



III. Method of fixing and staining . . 271 



IV. Spermatogenesis of Sympelrum semicinclum (Say) 273 



(a) Spermatogonial period 273 



(b) Growth period ... 275 



1. Formation of chromatin masses 276 



2. Leptotene stage 276 



3. Synapsis 277 



4. Synizesis 277 



5. Segmenting of spireme 277 



6. Formation of crosses 278 



(c) First spermatocyte or maturation division 279 



(d) Second spermatocyte division 281 



(e) Transformation of spermatids 282 



V. Some Notes on Libellula basalis 284 



VI. Historical review of papers on dragon-flies 286 



VII. General Considerations 288 



VIII. Summary 289 



Bibliography .... 290 



Plates 292 



Observations upon the changes which occur during the ripen- 

 ing of the male sex products in Sympetrum semicinctum (Say) 

 are described in this paper. The account, beginning with the 

 last multiplication division of the spennatogonia, traces especially 

 the behavior of the chromatin through the growth and matura- 

 tion periods up to and including the formation of the spermatozoa. 



The sex-chromosome, a round, univalent body, appears at the 

 beginning of the growth period and by its different staining 

 capacity can be traced as a definite body throughout the changes 



269 



