Studies on Chromosomes 19C 



inal chromosomes is lost in the ''resting" nucleus after each mito- 

 sis, each new chromosome nevertheless arises by a kind of endog- 

 enous formation within and from the substance of its predecessor. 

 In this way an individual genetic continuity of the chromosomes 

 can be directly followed through the "resting period" of the nu- 

 cleus. " Eine genetische Kontinuitat der Chromosomen nacheinan- 

 der folgender Mitosen konnte in der von mir untersuchten 

 Objekten teils sicher (AUium, Amphiuma) teils mit iiberwiegen- 

 der WahrsheinHchkeit (Ascaris) verfolgt werden. Es ging aber 

 auch hervor, dass eine Identitdt der Chromosomen verschiedener 

 Mitosen nicht existiert, sondern dass jedes Chrornosom in einem 

 friiher existierenden endogen entstanden ist, um wieder am Ende 

 seines Lebens fiir die endogene Entstehung eines neuen Chromo- 

 soms die Grundlage zu bilden" (op. cit, p. 54). Whether this 

 particular conclusion will also apply to more slowly dividing cells 

 remains to be seen. But apart from this direct evidence it seems 

 to me that a denial of every form of genetic continuity between 

 the chromosomes of successive cell-generations — ^which, despite 

 certain quahfications, seems to be the position of Fick and a num- 

 ber of other recent writers — is only possible to those who are ready 

 to ignore some of the most obvious and important of the known 

 facts, especially those that recent research has brought to hght 

 among the insects. The most significant of these are : 



1 In Metapodius the specific number varies, while in the indi- 

 vidual both the number and the size-relations of the chromosomes 

 are constant. 



2 In all species where the somatic chromosome-groups show 

 sexual differences in regard to the number and size-relations of 

 the chromosomes, exactly corresponding differences exist between 

 the male-producing and the female-producing spermatozoa. 



Both these series of facts demonstrate that the "tactic forma- 

 tion" of a fixed number of chromosomes of particular size is not a 

 specific property of a single chromatin-substance as such, of the 

 species. It has been assumed by some writers that departures 

 from the normal specific number, such as appear in merogonic, 

 parthenogenetic, double-fertilized or giant (double) eggs, are the 

 result merely of departures from the normal quantity of chroma- 



