270 ELIZABETH A. SMITH. 



which take place in the nucleus, from the pre-synaptic period 

 up to the formation of the spermatid, where it loses its identity 

 and combines with the chromatin derived from the autosomes. 

 The exact behavior of the autosomes is difficult to make out in 

 all details. They apparently unite by a side to side union, or 

 parasynapsis, and later separate along the line of union to form 

 rings which condense into quadripartite elements. 



For comparison, another species of dragon-fly, Libellula 

 basalis, was also studied. 



To Professor M. F. Guyer, under the direction of whom the 

 present problem was undertaken, the writer is indebted for help 

 and criticism. For the identification of the species of nymphs, 

 thanks are due Mr. R. A. Muttkowski. 



I. NYMPHS. 



Several hundred nymphs of two species, Sympetrum semi- 

 cinctum and Libellula basalis, were collected in the spring and 

 fall of 1912. Most of those obtained in the spring were found 

 in the ooze of the marsh before they had come up for transforma- 

 tion. In the fall, the majority were found clinging to reeds and 

 roots of grasses along the bank of a little stream on the Uni- 

 versity farm. The most prevalent form was Sympetrum semi- 

 cinctum (Say). See Fig. I, for a drawing of a nymph. A large 

 number of nymphs secured early in the spring, 8 to 10 mm. 

 long, must have belonged to the brood of the preceding year. 

 Other nymphs taken in the spring measured 17 or 18 mm. 

 Some of these had well-developed testes and were about ready 

 to transform, while others had no visible gonads. Of the 

 nymphs obtained in the fall, many were small and had evidently 

 hatched from eggs laid during July or August, while most of 

 the large ones had reproductive organs just developing. These 

 facts indicate that the larval period extends over more than one 

 year. 



II. TESTES. 



The testes of the nymphs appear as two white filaments, one 

 on either side of the digestive tract, extending almost the entire 

 length of the abdomen. They are not composed of lobules like 



