530 A. C. WALTON 



exclusively morphological- point of view. Nelson, Bischoff and 

 Thompson maintained that the sperm came in contact with, 

 but did not enter, the egg. Meissner believed that the sperm 

 entered the egg through a micropyle, and in this view Munk 

 ('58) concurred. Claparede ('58) denied the existence of a micro- 

 pyle, and thought that the sperm could enter the egg at any 

 point. 



The work of Van Beneden ('83), ('87), Carnoy ('86) and Boveri 

 ('86) showed that the ascarids are very favorable for cytological 

 study. In the next thirty years practically every known species 

 of parasitic nematodes was subjected, at least casually, to a 

 cytological investigation, in order to corroborate or combat the 

 evidence derived from A. megalocephala by the writers last 

 mentioned and their numerous followers. 



Carnoy ('87) was the first to examine carefully the gameto- 

 genesis of the ascaris of the dog, which he refers to as possibly 

 being A. marginata Rud. Kultschitzky ('88 c) and Lukjanow 

 ('89) also carefully studied dog parasites, which they believed 

 to be A. marginata Rud. None of these three investigators 

 arrived at the same conclusions regarding either the number of 

 the chromosomes or the method by which reduction to the hap- 

 loid number was effected, although each was supposed to have 

 used the same species of nematodes as the other two. Carnoy 

 ('87) found four chromosomes as the haploid number in each sex. 

 At the formation of the first polar cell, four of the eight diploid 

 chromosomes were eliminated. At the second division half of 

 each of the remaining four chromosomes was cut off in the sec- 

 'ond polar cell, leaving four female chromosomes to enter into 

 the composition of the segmentation nucleus with the four 

 brought in by the spermatozoon. 



Kultschitzky ('88 c) worked only on the oogenesis of A. mar- 

 ginata; he found twenty-two diploid chromosomes, which be- 

 came reduced by the two maturation divisions to eleven haploid 

 chromosomes. Lukjanow ('89) also followed Rudolphi in call- 

 ing the ascaris of the dog A. marginata, but stated that A. 

 marginata Rud. ('01), A. mystax Zeder ('03), and A. canis Wer. 

 ('85) were all the same species. Lukjanow found that the di- 



