222 SOME PROBLEMS OF CELL-ORGANIZATION 



form an apparently homogeneous body. In the chromosomes of 

 the germ-nuclei the number is at least double this (Van Beneden). 

 Their number has been more carefully followed out in the sperma- 

 togenesis of the same animal (variety bivalens) by Brauer. At the 

 time the chromatin-grains divide, in the reticulum of the spermato- 

 cyte-nucleus, they are very numerous. His figures of the spireme- 

 thread show at first nearly forty granules in linear series (Fig. 92, A). 

 Just before the breaking of the thread into two the number is 

 reduced to ten or twelve (Fig. 92, C). Just after the division to form 

 the two tetrads the number is four or five (Fig. 92, D), which finally 

 fuse into a homogeneous body. 



It is certain, therefore, that the number of chromomeres is not con- 

 stant in a given species, but it is a significant fact that in Ascaris the 

 final number, before fusion, appears to be nearly the same (four to 

 six) both in the oogenesis and the spermatogenesis. The facts re- 

 garding bivalent and plurivalent chromosomes (p. 61) at once sug- 

 gest themselves, and one cannot avoid the thought that the smallest 

 chromatin-grains may successively group themselves in larger and 

 larger combinations of which the final term is the chromosome. 

 Whether these combinations are to be regarded as " individuals " is 

 a question which can only lead to a barren play of words. The fact 

 that cannot be escaped is that the history of the chromatin-substance 

 reveals to us, not a homogeneous substance, but a definite morpho- 

 logical organization in which, as through an inverted telescope, we 

 behold a series of more and more elementary groups, the last visi- 

 ble term of which is the smallest chromatin-granule, or nuclear 

 microsome beyond which our present optical appliances do not allow 

 us to see. Are these the ultimate dividing units, as Brauer suggests 

 (p. 79) .? Here again we may well recall Strasburger's warning, and 

 hesitate to identify the end of the series with the limits reached by 

 our best lenses. Somewhere, however, the series must end in final 

 chromatic units which cannot be further subdivided without the 

 decomposition of chromatin into simpler chemical substances. These 

 units must be capable of assimilation, growth, and division without 

 loss of their specific character. This I believe is an absolute logical 

 necessity. It is in these ultimate units that we must seek the 

 "qualities," if they exist, postulated in Roux's hypothesis; but the 

 existence of such qualitative differences is a physiological assump- 

 tion that in no manner prejudices our conclusion regarding the 

 ultimate viorpJiological composition of the chromatin. 



