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
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