156 EZRA ALLEN 



Sobotta and Burchard ('10) state that the number in the egg 

 is 32, but they admit great difficulty in arriving at this con- 

 clusion and confess to some uncertainty. They declare with 

 assurance only that there are 8 in each daughter cell of the second 

 "division, explaining this number as a second reduction. 



Other rodents in which the number of chromosomes have been 

 reported are: 



Guinea-pig, Stevens ('11), probably 56; X and Y present. 

 Rabbit, Bachhuber ('16), probably 22; X and Y present. 

 Mouse, Sobotta ('95), 24; no mention of accessory. 



Of the other mammals for which the number of chromosomes 

 has been reported we have: 



Bull, Schoenfeld ('02), 24 or 25, probably 25. 

 Opossum, Jordan ('12), 18; X present. 

 Pig, Wodsedalek; ('13), 18; X and Y present. 

 Horse, Wodsedalek ('14), 37; X present. 



The number for man has been given so variously that I have not 

 included the different references in the foregoing list. All one 

 can say at present about it from the literature is that it varies 

 from 12 to 48. 



In general a rather high number prevails in mammals. I have 

 examined briefly slides made from guinea-pig and mouse testes 

 and find the large number very manifest, though I have not 

 attempted actual counts. The chromosomes seem better differ- 

 entiated in the former in each stage and consequently easier of 

 study than in the rat. 



The wide variations of the number recorded in man seem due 

 in part to the difficulty of getting fresh material and in part to 

 the unfavorable reaction of the tissue to the traditional fixatives 

 and technique. In view of the recent experiments of Hance 

 ('17), Whiting ('17), and Carothers (MS.) on fixation of insect 

 and mammalian testes, it would seem that the whole problem 

 of mammalian spermatogenesis is to be solved by better tech- 

 nique. The results of these workers agree with my own experi- 

 ence. Good technique gives chromosomes much more clearly 

 separated and consequently more workable than poor technique. 

 It is quite likely that Sobotta's double reduction is apparent 



