554 A. C. WALTON 



2. Second maturation division' 



The telophase of the first division merges imperceptibly into 

 the prophase rearrangement of the chromosomes of the second 

 maturation spindle, there being no pause to mark the separation 

 between the two stages. The new spindle (fig. 46) is at once 

 set up, and the eighteen tetrad chromosomes arrange themselves 

 in the metaphase plate. The spindle then undergoes a rotation 

 of ninety degrees and comes to rest with its long axis perpen- 

 dicular to a tangent to the surface of the egg at that point (fig. 

 47). In the formation of the second maturation spindle no 

 centrosomes can be made out — only the centrioles, and these 

 but faintly. 



As was the case in the first division of the oocyte, and also in 

 the case of the second spermatocyte (Walton, '16 a , the divi- 

 sion is longitudinal (fig. 48). The centrioles are faintly visible 

 and the spindle fibers are uniformly distributed (fig. 49). The 

 second division is clearly shown to be longitudinal. This divi- 

 sion is along the plane of the original parasyndesis of the first 

 oocyte prophase chromosomes, and hence separates parts thsrt 

 are not alike — unless an improbable synmixis has taken place. 

 Such a separation would result in a distribution of unlike parts to 

 the daughter chromosomes, and so would be a reduction in the 

 Weismannian sense, a reduction such as is denied for Nematodes, 

 especially for Ascaris megalocephala, by most writers, Griggs ('08) 

 and a few others being the only exceptions. Griggs favors a pre- 

 reduction after metasyndesis. Tretjakoff ('04 b) finds post-reduc- 

 tion after parasyndesis in the male of A. megalocephala, and both 

 Fick ('08) and Meves ('08) believe a true reduction occurs in 

 the prophase. Vejdovsky ('07) and others contend that there is 

 no true reduction in A. megalocephala. A Weismannian re- 

 duction by means of post-reduction (transverse division) after 

 telosyndesis is asserted by Marcus ('06) to occur in A. canis (?). 

 Study of material from what is believed to be the same species 

 of dog ascaris that Marcus used shows that, though Marcus was 

 right in the idea of the nature of the reduction, he was probably 

 mistaken in his idea of telosyndesis. 



