204 CHARLES L. PARMENTER 



about one another is plainly evident in Mev'es' ('11) figures 11 

 to 15 which show each chromosome to be of variable width. 

 These figures are exactly comparable to my figures 1 to 8, and 9 

 to 23 which demonstrate that this variation in width is due to 

 the twisting of the chromatids. Delia Valle represents each 

 chromosome to be of uniform width excepting an occasional 

 split in the end of some chromosomes. If he does not see chro- 

 matids in any of the chromosomes which he has drawn, either 

 his observations, his technique, or both are faulty. Further- 

 more, the above evidence together with his attitude make it 

 uncertain whether his preparations were as clear or the chromo- 

 somes as distinctly separated from one another as his drawings 

 indicate. 



Finally, Delia Valle's above demonstrated attitude, the ab- 

 sence of confirmatory evidence for his contentions, his question- 

 able ability as an observer as indicated by his drawings, and the 

 results of critical counts in Ambystoma tigrinum, all support 

 the view that his observations and conclusions are incorrect. 



But upon the assumption that they may be partially correct, 

 there are some possible explanations for the presence of variation 

 in the peritoneum of Salamandra maculosa. 1) One or more 

 chromosomes of a complex easily could have been disturbed, as 

 is evident from my figures 22 and 24 to 26. This could account 

 for number deficiencies and perhaps also for excesses. 2) 

 Champi ('13, p. 181) claims that chromosome number can varj- 

 by fragmentation under the influence of certain external stimuli. 

 Delia Valle (''09, p. 86) says the number of mitoses can be in- 

 creased by keeping the larvae covered with a blue glass. If 

 Delia Valle did this, and if such a stimulus could produce frag- 

 mentation, a bare possibility is offered for a disturbance of 

 chromosome number. 3) There is also a slight possibility that 

 the larvae had been kept in captivitj'- and might in consequence 

 have been sufficiently pathological to produce abnormal mitoses. 

 4) In an investigation on certain Orthoptera now in progress in 

 this laboratory, Mr. Carroll observes that in three individuals 

 some of the few dividing spermatogonial cells contain, in ad- 

 dition to the normal number of twentj-three, one, and some two 



