154 M - xv - W.ACKMAX. 



displays unmistakable individuality all of the chromosomes pos- 

 sess individuality. This argument has been made in other cases 

 and, while the continuity of the accessory chromosome does offer 

 valuable evidence in support of the individual continuity of the 

 chromosomes in general, it cannot be said to establish the truth 

 of the general theory. 



The difficulty of establishing the individuality of the chromo- 

 somes during the growth period would seem fully as great as 

 during the spermatogonial period. During all the stages in which 

 the karyosphere exists the chromosomes are so densely aggregated 

 that it is impossible to distinguish the separate elements. But 

 even at this time it is possible in favorable cases to distinguish 

 the accessory chromosomes and to discern the outlines of some 

 of the other elements. Furthermore, as I have shown in previous 

 papers (Blackman, 105, op. cit.) the chromosomes enter the karyo- 

 sphere as distinct bivalent elements, and at the end of the growth 

 period arise from it as distinct chromatic segments of the same 

 number and character as in the earlier stage. 



The chromatin segments entering the karyosphere are bivalent 

 threads formed by the union and subsequent diffusion of two 

 spermatogonial chromosomes. The point of union of synapsis 

 shows very plainly as a distinct interruption of the chromatin 

 granules near the middle of the segment, the interval being 

 bridged by linin fibers. In favorable sections of the karyosphere 

 (i. e., those in which the stain has been sufficiently extracted) it 

 is seen that this body is made up of a number of chromatin seg- 

 ments closely massed about the accessory. The chromosomes 

 on leaving the karyosphere are of the same structure as when 

 they entered, are of the same number and in appearance differ 

 from those of an earlier period in size only. In fact, the larger 

 spermatocyte chromosomes possess nearly as great a bulk as the 

 entire chromosome group of the spermatogonium, this immense 

 increase in size being accompanied by a growth of other parts of 

 the cell, which is proportionally even greater. 



It would appear then, that during certain stages of the sper- 

 matogenesis of Scolopendra it is possible to demonstrate absolutely 

 that each chromosome is a distinct unit rhararteri/ed by certain 

 definite and constant peculiarities and that the continuity of 



