GERM CELLS IN ASCARIS INCURVA 71 



X-components possibly excepting Acholla, do not act as a unit 

 until the time of the second, in this case the unequal, division, 

 moreover, so far as can be judged from the figtires the Y is not 

 definitely mated to any one member of the X-group. 



The genus Ascaris, as pointed out by Wilson ('11) in the case 

 of Ascaris megalocephala, gives some basis for the suggestion 

 of Stevens ('06) that an unmated X may form by release of 

 X-chromatin from a Y-YX bivalent thus leaving the Y-Y por- 

 tion to function as a bivalent and the X-chromatin as a univalent 

 chromosome. In Ascaris fehs the group is an unequal tetrad, 

 the larger component not being visibly compound; in Ascaris 

 incurva the X-element is clearly compound but still united to 

 the Y-Y portion; Ascaris megalocephala shows an X-element 

 sometimes united and again separate from the Y-Y (?) chromo- 

 somes which are in this case recognized as autosomes; while in 

 Ascaris lumbricoides it may be that the separation of the com- 

 pound X from the Y-Y pair has taken place. In this respect 

 the chromosome complex of the genus Ascaris most closel}' 

 resembles that of Orthoptera such as Hesperotettix, Anabrus 

 (McClung '05) or Leptnia (de Sinety '01) in the association of 

 the X with an autosome or a Y-Y (?) group. 



It may be argued that the condition in the above mentioned 

 Hemiptera — the non association of the Y, — elements with 

 each other and with the X-components is in some way correlated 

 with the disjunction of the XY complex in the second rather 

 than in the first division. Thus in these Hemiptera the X and 

 Y elements are distributed somewhat widely in the same plane 

 of the polar plate of the first maturation spindle and prepared 

 for an equatorial division, while in Ascaris incurva Y and YX 

 are opposed in position for a reducing division. Ascaris megalo- 

 cephala and Acholla multispinosa nlay represent intermediate 

 conditions, as in both of these forms there exists before the first 

 division a tendency towards association of X and Y components. 

 In Acholla the union is incomplete and disjunction of these 

 elements occurs in the second division; in Ascaris megalocephala, 

 when the X-element is separate, disjunction may occur in eithep 

 the first or the second division but its behavior when united is 



