532 A. C. WALTON 



plasmosome disappeared at the time of the formation of the 

 chromosomes of the first maturation spindle. The paired, split 

 threads upon becoming converted into compact chromosomes 

 again divided longitudinally, at right angles to the plane of the 

 first Separation, thus forming four-parted threads. These short- 

 ened and then by telosyndesis united to form eight-parted, or 

 octad chromosomes. In the oocytic and spermatocytic divisions 

 the chromosomes each divided longitudinally, the second matura- 

 tion division being the reduction division. There was no rest- 

 ing stage found between the first, and second divisions. The 

 centrosome was of intra-nuclear origin and continued from the 

 first to the second divisions unchanged. 



The two pronuclei did not fuse until after the setting up of 

 the first segmentation spindle. The centrosomes of this spindle 

 were derived from the one introduced by the sperm. Each of 

 the daughter cells of the first cleavage had eleven tetrad chromo- 

 sorpes — the result of the pairing of the eleven dyads (each of the 

 four elements of a tetrad dividing in the first cleavage). These 

 tetrad divisions were longitudinal. The second cleavage showed a 

 process of 'diminution' in the first soma cell, but none in the sister 

 cell — the stem cell. These stem cells continued to show eleven 

 tetrad chromosomes, while the soma cells showed twenty-two 

 dyad chromosomes. 



Medical writers had been differing greatly as to the identity 

 of the species of intestinal nematodes of the dog and the cat, 

 some claiming that the type found in the domestic cat was but 

 a smaller edition, so to speak, of the A. canis Wer. found in dogs. 

 Others maintained that it was an entirely separate species and 

 should rightfully be called A. felis Goeze. Glaue ('08, '09, '10) 

 made a very careful morphological and histological study of 

 both types — A. canis and A. felis — and came to the definite con- 

 clusion that these two parasitic nematodes were entirely differ- 

 ent species, viz. A. canis Werner and A. felis Goeze, not merely 

 varieties of A. mystax Zeder or A. canis Wer. Schoppler und 

 Krtiger ('12) took the opposite view and called the parasites of 

 both dog and cat A. canis Werner, in spite of the fact that the 

 work of Edwards ('11) had shown a cytological condition in A. 



