194 A. C. WALTON 



One case of an unattached idiosome was found, there being ten 

 diad chromosomes in the equatorial plate. A similar nucleus 

 in the anaphase condition showed the dividing idiosome lagging 

 behind the nine autosomes (fig. 11). 



The spermatids formed from both types of spermatocytes of 

 the second order show a clumped mass of chromatin with the 

 centrosome embedded in one side of this mass (fig. 12). There 

 is so little difference in the amount of chromatic material in the 

 spermatids arising by the division of the two types of second 

 spermatocytes, that there is no appreciable difference in size. 



DISCUSSION 



The results of Edwards ('11), closely approximated by the 

 earlier work of the present writer (Walton, '16 a), have been 

 checked carefully in this later examination of A. felis material 

 and have been found to be in the main faulty only because the 

 interpretations were based on too small an amount of material. 

 Edwards reported that polar views of the metaphase plates of 

 the first spermatocyte division showed nine tetrad chromosomes, 

 one of which was asymmetrical and larger than any of the re- 

 maining eight. This large tetrad was composed of two unequal 

 parts, the larger component being as large as one of the ordi- 

 nary tetrads. The smaller component was about half the size 

 of the autosome tetrads. The first division was transverse, and 

 separated the unequal components of the large tetrad, which 

 was undoubtedly to be classed as a sex chromosome, either of 

 the XY-type or as an X-chromosome attached to the end of an 

 autosome tetrad. Edwards inclined towards the first interpre- 

 tation. Boveri ('11), after a review of the evidence presented 

 by Edwards, advocated the second interpretation. 



In the first division one daughter plate received eight diad 

 autosomes and the larger (X) component of the heterochro- 

 mosome; the other plate received eight autosomes and the 

 smaller (Y) component of the heterochromosome. The second 

 spermatocyte division was equational and regular, each sper- 

 matid receiving nine chromosomes (eight plus either X or Y). 

 The spermatid receiving the X-chromosomes showed eight 



