472 Alice M. Boring 



period and do not divide in either spermatocyte division, as the 

 other 19 chromosomes do, thus appearing in only one quarter of 

 the spermatozoa, Wallace concludes that all the spermatozoa 

 degenerate except those v^ith the two odd chromosomes. 



Montgomery in Lycosa ('05) finds an even number of chromo- 

 somes in the spermatogonia. Two of these he calls heterochromo- 

 somes, although the only characteristic that justifies this name is 

 that they remain condensed in the growth period. They conju- 

 gate like the other chromosomes and divide in both divisions, all 

 of the spermatozoa receiving one-fourth of the heterochromosome 

 tetrad. 



The results of neither of these investigators agree with the more 

 recent work on the odd chromosome in spiders and other forms. 

 If, as Wallace states, no spermatozoa develop except those con- 

 taining the two odd chromosomes and the nineteen ordinary 

 chromosomes, the eggs must all contain only 19 chromosomes, as 

 the spermatogonial number is 40. Suppose each egg to have 19 

 chromosomes; fertilization by a spermatozoon with 19+2 chromo- 

 somes would give all the offspring 38+2 (19+2 in the reduced 

 number), whether male or female; but according to Wallace's con- 

 tention, the egg can have only 19; therefore it is impossible that 

 all the spermatozoa, except those with the two odd chromosomes, 

 degenerate. According to Montgomery, the heterochromosome 

 in the spermatocyte is bivalent and divides in both divisions. 

 Berry's work ('06) brings the odd chromosome in the spider into line 

 with the odd chromosomes in other forms; it is a single chromo- 

 some in the spermatogonia, and divides in only the second divi- 

 sion of the spermatocytes, resulting in dimorphism of the sper- 

 matozoa. 



Myriapoda 



Blackman ('05a, '05b) finds in Scolopendra heros and S. sub- 

 spinipes an uneven number of spermatogonial chromosomes. 

 Synapsis takes place in the late anaphase of the last spermatogonial 

 division, all of the chromosomes uniting in pairs except the odd 

 one. The odd chromosome divides only in the second spermato- 

 cyte division. The peculiarity here is that the other chromosomes 



