THE CHROMOSOMES OF THE CERCOPID/E. 135 



OBSERVATIONS ox CHROMOSOME INDIN inr AI.H v. 



The chromosomes of Philcenits are more like those of tin- 

 three forms studied at Cold Spring Harbor than like the one 

 worked on by Dr. Stevens at Harpswell. The abundance of the 

 material and the large size of the chromosomes in the aceto- 

 carmine preparations have made it possible to study the indi- 

 viduals in this form more accurately than previously in the other 

 forms. 



The equatorial plates of the primary spermatocytes ahvav- 

 show 12 chromosomes (Figs. 1-7) and the secondary spermato- 

 cytes ii and 12 (Figs. 8 and 9). The odd chromosome usually 

 stands to one side of the primary spermatocyte plate, when it is 

 in the same plane (Figs. 1-7, X), but it very often lies in an 

 entirely different focus, at the end of the spindle (Figs. 10, n, 12). 

 It is always one of the smallest chromosomes. It is impossible 

 to individualize each of the twelve chromosomes, but each plate 

 shows one largest (A), two almost as large (B, C), several inter- 

 mediate, and three or four smallest, one of which is the odd 

 chromosome. The secondary spermatocyte plates show the 

 same condition, one largest chromosome and two almost as 

 large, but here in the plates with n chromosomes (Fig. 9), there 

 is, of course, no odd chromosome and in the plates with 12 (Fig. 

 8), it has no particular position by which it can be identified. 



The individuality of these chromosomes can be traced also in 

 the prophase of the first spermatocyte division (Fig. 15). The 

 odd chromosome is a single round body, while the others are 

 already split for the first spermatocyte division. Among these 

 dumbbell-shaped bodies the one largest and the two chromo- 

 somes almost as large are clearly recognizable (Fig. 15, A, B, C). 

 In the side view of the metaphase figure the odd chromosome 

 still appears round and undivided alongside of the other dividing 

 chromosomes (Fig. 16). It is here about the size of half of one 

 of the smallest bivalent chromosomes, so we could expect it to be 

 undifferentiated by size from the smallest ones in the end view 

 of the equatorial plates, as has been previously described. 



In anaphase, the odd chromosome lags behind the others, but 

 goes undivided to one pole. Its small size is again evident here 

 (Fig. 17). The second spermatocyte division follows close after 



