OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 543 



of the male of A. canis, as shown by the writer (Walton, '16 a). 

 However, in the male sex cells two masses of chromatin and linin 

 instead of one are found. One of the two contained the com- 

 ponents of the heterochromosome group, while the other con- 

 tained all the autosomes. In the primary oocytes the compo- 

 nents of the heterochromosome group, which is of the '2X' 

 character, are not so differentiated from those of the autosomes 

 as are those in the male; but all are united into a single group, 

 in which it is impossible to recognize individual elements. From 

 analogy with the male one might infer that it is these hetero- 

 chromosomes that, after their differentiation, are the first to 

 move toward the center of the nucleus, just as the heterochro- 

 mosomes are known to do in the case of the male sex cells; but 

 no satisfactory evidence is at hand to support this hypothesis. 



The direct formation of the chromosomes from the chromatic 

 mass, that is without the intercalation of spireme threads, also oc- 

 curs in the case of A. marginata (Kultschitzky, '88 c, p. 673), where 

 the chromosomes are described ''als Resultate dessen ein pro- 

 gressives Zerfallen des Chromatinkliimpchens in ein Haufchen 

 einzelner Korner .... sich einstellt." Although Kult- 

 schitzky makes no statement as to t^e number of chromosomes 

 formed, h« pictures twenty-two in the majority of the cases 

 figured, namely figures 11 to 14. Lukjanow ('89) also worked 

 on A. marginata, but came to an entirely different conclusion 

 both as to the method of the formation of the chromosomes, 

 and as to their number. However, in agreement with Kult- 

 schitzky, he states that the spireme stage is entirely missing. 

 He finds that eight bivalent (dyad) chromosomes are formed by 

 the secretion of 'hyaloplasm' around small chromatic karyo- 

 somes which appear suddenly in the ground substance of the 

 nucleus. One member of these dyad-like pairs is always slightly 

 larger than its mate. The presence of the dyads is due to a 

 process of 'pseudo-reduction,' by synapsis, to the haploid num- 

 ber, which occurred before the definite appearance of the 

 chromosomes. 



Marcus ('06, p. 445) describes a single spireme thread ''der 

 deutlich langsgespalten ist" even before it enters into a clumped 



