SPERMATOGENESIS OF THE GALL-FLY, 35 



mounted in euparal. Euparal offers several advantages over 

 balsam as a mounting medium. Thus its use obviates running 

 stained sections through absolute alcohol; since sections may be 

 transferred directly from 95 per cent, alcohol to euparal. Next 

 the index of refraction of euparal is low i .483. And lastly euparal 

 dries quickly, so that sections may be studied at the end of twelve 

 to twenty-four hours after mounting, without danger of injury. 



Observations. 



The testes of the late larva and early pupa show primary 

 spermatocytes at the end of the growth period as large polygonal 

 cells having a reticulated nucleus containing a poorly defined 

 nucleolus, often of a bipartite character (Fig. i). The nucleolus 

 does not take the safranin stain as deeply as the chromosomes, 

 and thus differs markedly from the chromosome nucleolus of the 

 primary spermatocytes of many Hemiptera. 



A true primary spermatocyte division does not occur. Instead,, 

 a small mass of cytoplasm free of chromatin is constricted off,, 

 forming the so-called polar body. Preparation for this sup- 

 pressed or abortive division begins with a change in the outline 

 of the cell, the spermatocyte assuming a pear shape (Figs. 2, 3 

 and 4). From the narrow end of the cell and forming the stem of 

 the pear, extends a short filar process. At the base of this process, 

 which at first glance suggests the tail of a spermatozoon, is often 

 found a light basic-staining spherule which may or may not be a 

 centrosome. While these changes are taking place in the cyto- 

 plasm the nucleus undergoes a slight contraction and the chro- 

 matin passes through a series of transformations terminating in 

 the formation of chromosomes (Fig. 4). 



The next step in the process is somewhat uncertain and there 

 may be some question as to seriation. It seems that after the 

 chromosomes are completely formed, they become massed in 

 clumps at one side of the nucleus, and from these masses distinct 

 loops extend toward the opposite side of the nucleus (Figs. 5 

 and 6). The cell shortens, the filar process becomes less distinct 

 (Fig. 6), and a portion of the cytoplasm is constricted off (Figs. 7 

 and 8). As this is taking place the nuclear membrane appears 

 very irregular in outline but seems to remain intact. Inside the 



