S8 bulletin: museum of comparative zoology. 



plainly distinguishable from one another, and each appears to be com- 

 posed of a much convoluted and tangled chromatin thread, which is 

 bound into a more or less compact mass by linin fibrils. Although, 

 it is impossible to count these masses accurately owing to the great 

 difference in their size and to the fact that a cross section of all cannot 

 be obtained in the same plane, their number is undoubtedly approxi- 

 mately that of the autosomes of the spermatogonia. Moreover, the 

 masses of chromatin have approximately the same orientation that 

 the autosomes had during the preceding telophase of the last sperma- 

 togonial division. For these reasons I believe we are justified in con- 

 cluding that each of these masses represents a univalent autosome. 

 Later, each mass becomes converted into a single chromatin thread 

 by a sort of unraveling process. In Figures 43 and 44 (Plate 3) four 

 of these masses are drawn in detail. This is a slightly later stage than 

 that shown in Figure 41, and the method of formation of the chroma- 

 tin thread is well shown. If each of these masses represents, as I 

 believe, a univalent chromosome, then it is evident that during this 

 stage each chromosome becomes converted into a long thread com- 

 posed of a single row of chromatin granules imbedded in a linin matrix. 

 In the following stage (c) these threads become evenly distributed 

 through the nucleus, giving the appearance of a very tortuous but 

 continuous spireme, and they have been so interpreted by most investi- 

 gators. There is, however, no e\ddence that such is the case. In the 

 next stage, which rapidly follows this, the spireme, just as in Dissos- 

 teira, is made up of loops the ends of which are attached to the nuclear 

 membrane at the distal pole. Since the number of loops even at this 

 early stage is, I believe, only one-half that of the autosomes in the 

 spermatogonia, it is probable that during stage c, or earlier, the chro- 

 matin threads unite in pairs end to end to form loops, while the oppo- 

 site ends become attached to the nuclear membrane at its distal pole 

 However, it is impossible to say precisely when the conjugation of the 

 autosomes takes place. Possibly it may occur as early as stage h, 

 as I have in a few cases seen structures which might be interpreted 

 as the result of the fusion of two chromatin masses end to end; but 

 as such structures may be only accidental, I have not thought it best 

 to attach any weight to them. 



2. Monosome. 



The history of the monosome during the growth period is practically 

 the same as in Dissosteria. 



