195 



is rather curious. Why "must" a tetrad be equal to -r ? Why "must" 



four be equal to two in order to satisfy the conditions of the case? 



In my first paper on the subject ('95, p. 9—13) it is stated that 

 in the spermatogonia there are 12 univalent chromosomes which 

 divide longitudinally or by the equation division of Weismann. 

 In the growth-stage, during which the spermatogonia become the 

 spermatocytes, the chromatic granules group themselves into 24 chromo- 

 somes. These 24 chromosomes become arranged in pairs, the indivi- 

 dual chromosomes of each pair being connected with each other by a 

 considerable number of linin threads. Later the pairs become asso- 

 ciated together in tetrads by a process of conjugation. From this con- 

 jugation we get as a result the quadrivalent chromatic rings of vom 

 Rath. In the first maturation division these tetrads are separated, 

 each into two bivalent chromatic bodies which consist of two chromo- 

 somes held together by linin threads. During the next division these 

 pairs of chromosomes are separated into single chromosomes. The 

 number of chromosomes in the spermatogonia as well as in the so- 

 matic cells is 12. During the prophases of the first division of the 

 spermatocytes 24 chromosomes appear in the form of 6 tetrads. The 

 spermatocytes of the second order receive each 12 chromosomes in 

 the form of 6 pairs of chromosomes. Finally the spermatids receive 

 6 chromosomes. Or, to state the matter in still another way, the 

 normal number of chromosomes is at first doubled, and afterwards, 

 by the two maturation divisions, reduced first to 12 and then to 6. 



Now, if in the prophases of the first maturation division it were 

 true that, as Wilson attempts to explain my account, "the 12 dumb- 

 bell-shaped primary segments must therefore represent single chromo- 

 somes, not bivalent ones", it would manifestly be quite impossible for 

 the spermatids to receive each 6 chromosomes, without the assumption 

 of a splitting of the chromosomes. But I was unable to find any 

 evidence of a splitting of the chromosomes during the two maturation 

 divisions, and stated my belief that in my material it did not occur. 

 The original statement is therefore not self contradictory, but it evi- 

 dently would be contradictory, if the substitution of values proposed 

 by Wilson should be made. 



Wilson's arithmetical difficulties in understanding my account 

 are created by his own method of interpretation. In my first paper 

 ('95) I took some pains to make clear the assertion that in the spi- 

 reme stage of the spermatocytes of the first order 24 chromosomes 

 arise. Wilson's statement that "Each of these dumbbell-shaped bodies 



