Studies on Chromosomes 193 



has thus far been discerned. Such a difference does not appear 

 in the size of the animals, for there are large individuals with no 

 supernumeraries and small individuals that possess them. An 

 interesting field for experiment seems here to be offered. 



c The "Individuality" or Genetic Continuity of the Chromosomes 



It is in respect to this much debated hypothesis that the facts 

 observed in Metapodius seem to me most significant and important. 

 It is evident' that the whole series of relations are readily intelligi- 

 ble if the fundamental assumption of this hypothesis be accepted. 

 Without such explanation they seem to me to present an insoluble 

 puzzle. The disposition to reject this hypothesis that appears in a 

 considerable number of recent papers on the subject will doubtless 

 lead to more critical and exhaustive observation of the facts; but 

 when it goes so far as to deny every principle of genetic continuity 

 in respect to the chromosomes, it is, I believe, a backward step. 

 This reaction perhaps reaches a climax in the elaborate and 

 apparently destructive criticism of Fick ('07) who considers the 

 hypothesis to be thoroughly discredited, and believes his analysis 

 to justify the conclusion: "Dass weder theoretisch noch sachliche 

 Beweise fur die Erhaltungslehre vorliegen, sondern dass im Gegen- 

 theil unwiderleghche Beweise gegen sie vorhanden smd, so dass es 

 im Interesse der Wissenschaft dringend zu wiinschen ist, dass 

 die Hypothese von alien Autoren verlassen wird" ('07, p. 112, 

 italics in original). I incline to think that this sweeping judgment 

 would have carried greater weight had Professor Fick, in certain 

 parts of his able and valuable discussion, taken somewhat greater 

 pains in his presentation of facts and shown a more judicial temper 

 in their analysis. 12 To some of the objections and difficulties 



12 1 will give two specific examples of this. The experimental results of Moenkhaus ('04), on hybrid 

 fishes, which evidently form a strong support to the continuity hypothesis, are unintentionally but com- 

 pletely misrepresented in the statement at p. 75: "So berichtet Moenkhaus bei Fundulus-Monidia- 

 kreuzung (sic), dass sich die beiderlei (zuerst sehr verschiedenartigen) Chromosomen in der Regel 

 schon nach der zweiten Teilung nicht mehr unterscheiden lassen." But Moenkhaus's explicit statement, 

 based on the examination of "many thousand cells," is that even in the late cleavage "Nuclei showing 

 the two kinds of chromosomes mingled together upon the spindle are everywhere to be found" (op. cit., 

 p. 48). Fick evidently had in mind the fact that the paternal and maternal chromosomes do not as a 

 rule retain their original grouping after the first two or three cleavages. His actual statement, however, 



