OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 531 



ploid number of chromosomes was sixteen, and that one-half of 

 the number of chromosomes as well as one-half of the chromatic 

 matter was lost at each division of the oocyte, leaving only four 

 female chromosome elements in the mature ovum to unite with 

 the four from the male. • 



No further investigations, except by medical writers, were di- 

 rected toward either the taxonomy or cytology of the ascarids 

 of the Canidae and Felidae until 1906. Marcus ('06), following 

 the nomenclature of Werner ('85), called his material A. canis 

 Wer. (var. mystax) ; but he obtained the most of his material 

 from bears and lions, only a small portion of it being from dogs. 



He maintained that the unreduced number of chromosomes 

 in his material was twenty- two, thus corroborating the results 

 of Kultschitzky. Marcus further showed that of these chromo- 

 somes twenty were united into pairs, but that two remained 

 unpaired, so that each of the primary gametes, both oocytie 

 and spermatocytic, had ten bivalent and two univalent chropio- 

 somes. In the first maturation division the bivalents divided, 

 each daughter nucleus receiving half of each bivalent element, 

 while of the two univalents one passed to each of the daughter 

 nuclei without dividing. Each daughter nucleus thus received 

 eleven univalent chromosomes. The action of the unmated pair 

 of chromosomes suggests that of an 'X-Y' pair, but Marcus made 

 no mention of such possibility. These two chromosomes were 

 the largest in the mitotic figure (Marcus, '06, taf. 29, fig. 

 13). 



In the early spermatocytic and oocytie stages he found a 

 single, longitudinally split, spireme thread. This contracted into 

 the center of the nucleus and gave rise to a true plasmosome, as 

 well as a drop of tropho-chromatin, which was entirely eliminated 

 from the nucleus. The central mass of chromatin broke up into 

 parallel threads that, crossing one another at all angles, united 

 to form a reticulum, which had chromatin granules at each point 

 of intersection; the intervening internodes being composed of 

 linin. As these threads constricted, the granules united and 

 formed the prophase chromosomes. Each chromosome showed 

 distinct 'end to end' halves, connected by a linin bridge. The 



