B. F. Kingsbury 125 



anticipatory. It lias theoretical bearings on the meaning of the con- 

 stancy of the number of the chromosomes and their individuality. Great 

 as the evidence is, my inclination is to regard the generalizations as to 

 the imjDortance of a constancy in number of the chromosomes and the 

 adherence to that number in the mitoses of different cells in the organ- 

 ism, as yet unsafe. 



The same doubt may be applied to the question of the individuality of 

 the chromosomes, for which the evidence is not as strong. On the 

 basis of the individuality of the chromosomes rests the interpretation 

 of the reduction in number of the chromosomes as to a synapsis or a 

 joining together in pairs, so that each is bivalent. This view may be 

 purely hypothetical and unobserved, as in Moore's work, or based on 

 actual observation, as in Montgomery's. In Desmognathus there is no 

 evidence that the chromosomes of the spermatocyte are bivalent; nor 

 in other Amphibia do we find evidence reported, save perhaps by Eisen 

 in Batrachoseps where the chromoplasts may be interpreted as joining or 

 separating single chromosomes. In that case, however, the number of 

 chromosomes is one-half what it should be in that form. 



The third general feature that attracts attention is the existence of 

 the peculiar chromosomxC-forms that characterize the spermatocyte 

 divisions, among which may be included, tetrads, ring-forms, X-forms, 

 Y-f orms, and V-forms different from the V-shaped chromosomes of ordi- 

 nary mitoses. It seems likely that the differences which exist between 

 the spermatocyte divisions in different forms is due to minor modifica- 

 tions of the procedure, and that they are not intrinsic, so that if the 

 modifying causes could be recognized, the variations could be more 

 easily understood. 



As a peculiarity of the spermatocyte mitoses has been mentioned the 

 lack of a period of growth between them. The rapidity with which the 

 second division follows the first in spermatogenesis seems to vary. 

 Perhaps Scyllium, according to Moore's account, presents, among ob- 

 served forms, the most complete resting stage between the first and 

 second divisions. Here a complete resting period intervenes, with new 

 formation of chromosomes in the second division. In Mammals like- 

 wise there is apparently a new-formation of the chromosomes after a 

 resting period, Lenhossek, 96. 



In Amphibia there is encountered a step toward the shortening of the 

 interval. In Salamandra, according to Meves' account, a true dispirem, 

 not to say a reticulum, does not seem to exist, and in Desmognathus the 

 chromosomes remain distinct, though they become irregular and thread- 

 like. The second splitting, furthermore (if we may accept this inter- 



