318 THOS. H. MONTGOMERY, 



seem theoretically probable, certainly not as an elastic organ to push 

 the pairs of centrosomes apart, for the two pairs wander apart on 

 the surface of the nuclear membrane, which would necessitate any 

 connecting structure to be bent around the surface of this membrane. 

 In Pentatoma also I could find no central spindle present at this 

 stage, though in this form as in Feripatus there is a clear central 

 spindle in the spermatogonic divisions. Might this be found to be a 

 general distinction between the prophases of spermatogonic and 

 spet-matocy tic prophases ? It was noted that while the pairs of centro- 

 somes are migrating apart from one another, the pole fibres radiating 

 from them attain a size and distinctness which they do not show 

 again: might not these cytoplasmic radiations be the agency of the 

 movement of the centrosomes along the nuclear surface? 



b) The Nucleus. 



The prophase of the 1st maturation division becomes marked in 

 the nucleus by the chromatin staining more intensely, and by the 

 coming together of the chromatin granules to form an irregular reti- 

 culum (Figs. 127, 128), so that the linin threads become more evenly 

 covered with chromatin than in the rest stage. This corresponds in 

 point of time to the "dense spirem" stage, but in these spermatocytes 

 there is no stage of the formation of a continuous chromatin spirem. 

 Early in the prophase the nucleoli get much smaller, but a portion 

 of one or two of them may frequently be observed near the centre 

 of the nucleus until the time of disappearance of the nuclear mem- 

 brane. These nucleoli are connected with linin fibres. 



The apparent chromatin reticulum segregates into a number of 

 separate strands, the chromosomes (Figs. 129—131, 133, 134). Now 

 in the preceding rest stage the boundaries of the individual chromo- 

 somes are generally indistinct , owing to the loose arrangement of 

 their chromatin granules along linin strands, but in some cases out- 

 lines of portions of chromosomes can be distinguished (Figs. 102, 105, 

 Plate 20) ; that is to say, in the rest stage the chromatin granules do 

 not become so dispersed in the nucleus that the integrity of the 

 chromosomes is destroyed. Accordingly, in the prophase now under 

 description the chromation reticulum is probably only an apparent one, 

 being composed of overlapping and interlacing, but still not continuous 

 chromosomes: so that in the early prophase chromosomes are not 

 being produced by a segmentation of a continuous reticulum, but 

 chromosomes which had, by virtue of their persisting linin connections. 



