OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 533 



felis that was very different from that reported for A. canis 

 (Marcus, '06). Edwards found in A. fehs a hetero chromo- 

 some group, of which he gave two possible interpretations. 

 One, that toward which he inchned, was that the group was 

 made up of an 'X-Y' pair in which the 'X' was twice as large an 

 the ' Y' ; the other was that the group was of the simple 'X' type, 

 the 'X' being joined to the end of one of the autosomes. Boveri 

 ('11), under whom Edwards worked, held to the latter interpre- 

 tation. In the first division each of the eight bivalent chromo- 

 some pairs so divided as to give each of the daughter plates as 

 equal share, while the univalent 'X-Y' pair gave to one plate 

 'X' and to the other 'Y', In the second division 'X' and 'Y' 

 divided equationally (Edwards, '11, pi. 28, figs. 2, 4, 5). 



The apparent morphological and cytological differences be- 

 tween ^. canis and A. felis have been the subject of further 

 study by the writer (Walton, '16 a). The morphological differ- 

 ences given by Glaue have thus been substantiated, as was also 

 the cytological work Df Edwards on A. felis. The work of 

 Marcus ('06) on A. canis, however, was utterly at variance with 

 the writer's results from the study of spermatogenesis. The 

 present writer found thirty tetrad chromosomes — twenty-four 

 autosomes and six idiosomes — as the diploid number in the 

 male, and thirty-six in the female sex cells. By pseudo-reduc- 

 tion these were reduced (in the male) to twelve di-tetrad (eight- 

 parted) autosomes and six tetrad idiosomes — eighteen in all. 

 At the first spermatocytic division the twelve autosomes were 

 halved and the six idiosomes laggingly passed to one of the 

 daughter nuclei, giving rise to two types of secondary sperma- 

 tocytes; one having twelve, and the other eighteen tetrad chromo- 

 somes. At the second spermatocytic division each autosome 

 as well as each of the six idiosomes, w^as again halved, giving rise 

 to spermatids also of two types; one having twelve dyad auto- 

 somes, the other having twelve dyad autosomes plus six dyad 

 idiosomes-yeighteen dyads in each nucleus of this type. As 

 there was no elimination of chromatic matter during the meta- 

 morphosis of the spermatids into spermatozoa, the latter are of 

 two types, equal in number and differing from each other in the 



