I2O KATHARINE FOOT AND E. C. STROBELL. 



In Wilson's "Studies on Chromosomes, Nos. II. and III.," he 

 has published several text figures of Anasa tristis, including the 

 stages from the "contraction phase" of the first spermatocyte 

 to the anaphase of the second spindle, and also four spermato- 

 gonial groups in which he figures an odd number of spermato- 

 gonial chromosomes, i. e., 10 pairs, and one large unpaired 

 univalent, the odd or " heterotropic " chromosome. 



A study of a large number of smear preparations of the testes of 

 Anasa tristis has forced us to the conclusion that in the spermato- 

 genesis of this form there is no so-called "accessory chromosome " 

 no odd, "heterotropic" chromosome that the so-called 

 " chromosome nucleolus " of the rest stage is the homologue of the 

 nucleolus of the egg, that in its form and time of disappearance it 

 bears a striking resemblence to the plasmosome of the egg of 

 Allolobophora fcetida. Our observations and interpretations are 

 so at variance with the conclusions reached by the three cytolo- 

 gists who have studied this form, that we would hesitate to take 

 issue with such competent authority were we not able to support 

 our observations by a very large number of photomicrographs 

 of the preparations. We have already nearly 200 photographs 

 which seem to demonstrate beyond question the following points. 



That the so-called " chromosome nucleolus " of the resting 

 spermatocyte is morphologically the equivalent of a nucleolus, 

 that it is not a chromosome. Wilson has emphasized the evi- 

 dence of morphological likeness in his Fig. 2, b and c (" Studies 

 on Chromosomes, II."), in which he shows a structure which he 

 interprets as a chromosome and which has a marked morpho- 

 logical resemblance to his sketch of the " chromosome nucleolus " 

 in his Fig. a. 



It is significant that in Wilson's three figures of this early pro- 

 phase only 6 of the 1 1 bivalents are shown in two of his draw- 

 ings and only 7 in the third. In fact, not one of the investiga- 

 tors of this form has given a single figure of this stage in which 

 all the eleven chromosomes are shown. 



In our photographs, on the contrary, all the 1 1 bivalents are 

 in evidence, and not one of them resembles in the least the 

 " heterotropic " chromosome figured by Wilson. This holds 

 true for hundreds of cells in which all the eleven bivalents are 

 present and clearly defined. 



