OOGENESIS AXD EARLY EMBRYOLOGY ASCARIS 571 



idiosomes it is reductional, one daughter cell receiving none of 

 the 'X' group, the other, all six of its members. In the female 

 the first division is clearly equational for the majority of the 

 chromosomes, and apparently so for the rest. Although the 

 idiosomes can not be accurately distinguished from the autosomes, 

 by any criteria as yet found, it is entirely possible that the cases 

 where it is difficult to locate the plane of division may be those of 

 the idiosomes. In these chromosomes it is often difficult to dis- 

 tinguish the plane of the original longitudinal split, in each of 

 the two tetrads forming the pair, from the plane of parasyndesis, 

 also longitudinal in relation to the axes of the resultant di-tetrad. 

 From the evidence now available, it seems most probable that 

 in all of the chromosomes the first maturation division is equa- 

 tional in character, though the possibility that the division of 

 the idiosome pairs may be along the plane of parasyndesis — 

 hence reductional, as in the case of the male — can not be dis- 

 regarded. It is hoped that future study may clear up this 

 seeming anomaly, in which the 'reducing' division in the male 

 'X' group does not occur at the same stage that it does in the 

 female, whereas the 'reducing' division of the autosomes does 

 occur at corresponding stages in both sexes. 



As a result of the first division, therefore, the chromosomes 

 of any one of the second oocytes are like those of all the others, 

 the chromatin matter in each cell, however, being reduced to 

 one-half of its former amount. Each resultant chromosome 

 (fig. A, 7 a) is a tetrad, similar in appearance to those found in 

 the early prophase of the primary oocytes (fig. A, 3 a). It 

 shows a definite longitudinal constriction as well as a transverse 

 one, the Quefkerbe. The second division (fig. A, 8) is, like the 

 first, along a plane parallel to the long axis of the tetrads, but 

 perpendicular to the plane of the first one, and hence coincides 

 with the original plane of parasyndesis. B}^ thus separating 

 into dyads along such a plane, true reduction of chromatic 

 qualities in the Weismannian sense occurs. The resultant chro- 

 mosomes contain one-fourth the original chromatic material and, 

 theoretically at least, two sister dyads are qualitatively different 

 while quantitatively alike. 



