SUTTON : SPERMATOGONIAL DIVISIONS IN BRACHYSTOLA MAGNA. 141 



primary spermatogonia, giving the appearance of splitting and sur- 

 ronnding the latter. 



The primary spermatogonia preparing for division can hardly be 

 said to enter directly upon a jDrophase, for that term as I have used 

 it implies the presence of a spireme. I do not regard the resting 

 stage as belonging in the direct line of division of the cell, but rather 

 as a special condition into which the chromatin enters for the pur- 

 pose of preparing for the rapid divisions which follow, or, as in the 

 case of those found between cysts of older cells, to secrete matter for 

 the maintenance and extension of the cyst walls. 



The chromatin of the resting-cell is arranged in Hakes or patches 

 around the periphery of the nucleus, and these are connected with 

 one another by a few linin tibers. ( Fig. 2.) As the cell prepares to 

 enter upon tlie prophases, a number of changes are to be seen ; the 

 tlakes of chromatin begin to be less clearly defined (tig. 3), iiniti 

 fibers become more numerous, and slowly the cell acquires more 

 cytoi:)lasm. These changes jaroceed until the chromatin of the 

 nucleus has assumed a reticular arrangement similar to that of fig. 4, 

 after which it may fairly be said to enter upon the prophases. 



One of the earliest of these is shown in fig. o, where the chromo- 

 raeres are arranged in several (probably the chromosomic number) 

 moniliform threads, lying for the most part against the nuclear mem- 

 brane: and the linin fibers are either all included in this thread, or 

 are now so very minute as to escape observation. Fig. (3 shows another 

 step. The chromatic threads still lie on the periphery, but they have 

 grown shorter and thicker, and there is no longer any doubt that each 

 corresponds to a future chromosome. Here the linin has again come 

 into evidence. 



About this time a clearly defined longitudinal split appears in the 

 threads (fig. 7), and the shortening and thickening of the segments 

 continues until we get the condition shown in fig. 8 — a number of 

 short, thick, longitudinally split chromosomes almost ready for divi- 

 sion. These now assume the form of short double rods, smooth in 

 contour and apparently homogeneous in structure ; the nuclear mem- 

 brane is dissolved, the spindle appears, the chromosomes take their 

 place in the equatorial plate, and the cell is in metai3hase. (Figs. 9 

 and 10.) 



Primary .spermatogonia in any other phases than the resting stage 

 or early prophase are, in my material, extremely rare, and in the few 

 late prophases I have seen there is nothing to throw light upon the 

 origin of the centrosomes. I have seen the latter only in the ineta- 

 phase, where they are clear and sharp but very small. 



The next stage which came to my notice is shown in fig. 11. Here- 



