116 bulletin: museum of comparative zoology. 



own, thus forming a structure similar to a nucleus but containing only 

 a single chromosome." Kornhauser ('15, p. 408) says concerning the 

 spermatogonia of Hersilia: — "The telophase chromosomes become 

 gradually fainter in outline, and a clear area in the cytoplasm begins 

 to form about them. It is, I believe, the boundary between this clear 

 area and the more reticular cytoplasm which forms the new nuclear 

 membrane." Thus it will be seen that it is quite usual for telophase 

 chromosomes to form individual nuclei, which later fuse to form the 

 whole nucleus, and with Smalhvood ('05) we may accept this tendency 

 as an argument for chromosomal individuality. 



(2) Theories of continuity. Among those who support a theory of 

 continuity, there is not always agreement as to what structures are 

 carried from one cell-generation to the next. It is generally agreed 

 that the chromosomes are composed of at least two substances; the 

 chromatin and the ground substance (linin, plastin). Hacker ('04) 

 formulated the " Successionshypothese," stating that the persisting 

 structures of the chromosomes consisted of the "Grundsubstanz," 

 or achromatic part. Bonnevie ('08a) and others, on the contrary, 

 regard the chromatic substance as the persistent portion and the 

 achromatin as the temporary part of the clu'omosome. 



Vejdovsky ('07, '11-12) has evolved a most elaborate theory touch- 

 ing this problem. In his monograph of 1907, he based his conclusions 

 on a study of the ovogenesis and maturation of some annelids. He 

 concludes that the nucleus is derived from the chromosomes and from 

 them alone. He divides the interkinetic stages into two periods; the 

 one during which the nucleus is formed out of the chromosomes he 

 calls " katachromasis," and the one during which the chromosomes are 

 formed out of the nucleus he calls "anachromasis." In his later 

 monograph ('11-12) he analyses these processes still further and 

 attempts to describe in detail the events in the two periods. His 

 conclusions may be briefly stated as follows : — A chromosome is com- 

 posed of two substances, one a less deeply staining substratum, on 

 the surface of which is the other, the more deeply stainable chromatin. 

 In the early stages of katachromasis, the chromatin differentiates into 

 a spiral thread, or "chromonema," which is coiled about the surface 

 of the substratum. The substratum then dissolves, forming the 

 nuclear sap, or " enchylema." The chromonema further differentiates 

 into a finely coiled chromatic portion, inside of which is a linin core. 

 In this condition, he recognizes the anlage of the chromosome of the 

 succeeding generation. The linin substance of the chromonema is to 

 become the substratum of the future chromosome, and the finely 



