STUDIES ON CHROMOSOMES. 239 



little or no evidence of such an element as I have described 

 beyond what might charitably be regarded as a mere accident. 

 Although they say that "it is impossible to count chromosomes 

 accurately in this material," and that to attempt to work out a 

 continuous detailed history of spermatogenesis in the Barred 

 Plymouth Rock "would require a large amount of imagination" 

 they have not hesitated to label a number of their mass-effects 

 as containing "no possible X." While they assert that some 

 15 per cent, of their preparations show a possible X-like element, 

 85 per cent, do not. It is only a fair question to ask if this 85 

 per cent, shows anything else, and if the pictures they give are 

 a fair sample of the whole, I think any unbiased observer will 

 have to admit that they do not. 



I agree with them in finding that it is very difficult to get a 

 satisfactory count of chromosomes except in the most favorable 

 material. But even without an absolutely accurate count it 

 can be determined in many preparations of chicken testis that 

 there is one peculiar curved or bean-shaped element present un- 

 like the others which are round or oblong, and above all, an 

 element that behaves in a characteristic way. When such ob- 

 servations can be strengthened by further unequivocal cases 

 where a count is obtainable, then it seems to me that legitimate 

 conclusions can be drawn regarding what is the usual occurrence 

 in the material in question. The evidence as seen under the 

 microscope undoubtedly shows that there are sometimes such 

 fusions of the ordinary chromosomes as to reduce the count 

 and this is, as I have already maintained, a constant factor in 

 secondary spermatocytes but this by no means invalidates the 

 evidence regarding a special X-like element, inasmuch as fused 

 ordinary chromosomes would not frequently be mistaken for it. 



In doing cytological work I have always accepted as a working 

 maxim that preparations which show nothing definite must be 

 ignored and only those taken into account which have sufficient 

 distinctness to be capable of a reasonable interpretation. Almost 

 any cytological preparation I have ever seen and I have ex- 

 amined preparations of some of the best technicians in America 

 and Europe will show a number of dividing cells, let us say, 

 which can not be said to give evidence of anything much beyond 



