ASCARIS CANIS AND ASCARIS FELIS. 369 



component is about half the size of the autosome tetrads. The 

 first division is transverse, and separates the unequal components 

 of the large tetrad, or hexad, which is doubtlessly to be classed 



A 



as a sex-chromosome, either of the XY-type or as an X-chromo- 

 some attached to the end of an autosome tetrad. 



In the first division the one daughter plate receives eight diad 

 autosomes and the larger component of the heterochromosome, 

 and the other plate receives eight autosome diads and the smaller 

 component of the heterochromosome. The second spermatocyte 

 division is equational and entirely regular, each spermatid 

 receiving nine chromosomes. As there are two types of second 

 spermatocytes, there are also two types of spermatids formed, 

 one having nine chromosomes all of the same size, and the other 

 having nine chromosomes, one of which is larger than the other 

 eight. 



These results agree with those obtained by Edwards ('n) in 

 his work on A. felis, and indicate that in all probability the 

 form studied by the writer and by Edwards are the same form 

 of A. felis. Since the figures made from my slides are in all 

 respects similar to those published by Edwards, it was thought 

 unnecessary to reproduce them here. 



DISCUSSION. 



The present work shows A . canis different both morphologically 

 and cytologically from A. felis. It shows also that the Nema- 

 todes worked upon by Marcus were evidently not A. canis. 

 Marcus did not offer any taxonomic evidence that he was dealing 

 with A. canis, this being merely another case in which a cytolo- 

 gist has not given proper consideration to the systematic standing 

 of his material. The spermatocytes in the Nematodes described 

 in Marcus's work contained twelve chromosomes, ten bivalents 

 and two univalents, and no heterochromosome group. As errors 

 in observation can not account for such diversity, it is doubtless 

 due to differences in material. 



SUMMARY. 



The following are the most important points brought out in 

 this study: 



