194 



Obgleich ich es noch nicht versucht habe, Käfer, Krebse, Ver- 

 steinerungen u. dergl. mit Feilen zu präpariren, so glaube ich doch, 

 daß gerade zu diesem Zwecke sich Feilen ganz besonders eignen. 



Nachdruck verboten. 



Chromatic Tetrads. 



By E. V. WiLCox, Ph. D., College of Agriculture, Bozeman, Mont., U. S. A. 



On page 200 of Dr. E. B. Wilson's work on "The Cell in De- 

 velopment and Inheritance" ('96) is to be found a criticism of my 

 work on the origin of the chromatic tetrads in the spermatogenesis 

 of insects. Under the head of "The Formation of Tetrads by Con- 

 jugation" Wilson says: — 



"The most specific accounts of such a mode of origin have, how- 

 ever, been given by Calkins (earthworm) and Wilcox (grasshopper). 

 The latter author asserts ( ' 95) that in Caloptenus the spireme of the 

 first spermatocyte first segments into the normal number (twelve) of 

 dumbbell-shaped segments which then become associated in pairs to 

 form six tetrads. Each of these dumbbell-shaped bodies is assumed 

 to be a bivalent chromosome, and the tetrad formation is therefore 

 interpreted as follows: — 



abed — I ah — cd — M a \ h e\ f , ,, ^ , . 



7 — = 1 7 T^i • ^1 -^Tj "-TT ßtc. (tetrads). 



(spireme (segmented spireme) c \ d g \ h 



There is therefore no longitudinal splitting of the chromosomes. A 

 careful examination of the figures does not convince me of the correct- 

 ness of this conclusion, which is, moreover, inconsistent with itself 

 on Wilcox's own interpretation. Since each germ nucleus receives 

 six chromosomes, the somatic number must be 12, and Wilcox has 

 observed this number in the divisions of the spermatogonia. The 

 12 dumbbell-shaped primary segments must therefore represent single 

 chromosomes, not bivalent ones, as Wilcox assumes, and his primary 



tetrad must therefore be not — v—-,. as he assumes , but either t 



c \ d 



or (if we assume that the normal number of chromosomes undergoes 



a preliminary doubling) jA^-r- Until this contradiction is cleared up 



W^iLcox's results must be received with considerable scepticism." 



This, it seems to me, is an unnecessary complication of my ori- 

 ginal statement of the case. The arithmetic of the above quotation 



