538 A. C. WALTON 



has thrown no further light on this question of nuclear-mem- 

 brane formation. Goodrich ('14) finds that the oogonial chro- 

 matin in Ascaris incurva, as in A. canis, tends to divide en masse 

 rather than as individual chromosomes, and that the hetero- 

 chromosome group is not differentiated from the autosomes by 

 being formed from separate karyosomes. In Ancyracanthus 

 cystidicola (Mulsow, '12), as in A. canis, the heterochromosomes 

 in the female are not morphologically differentiated from the 

 autosomes, while they are in the male. Angiostomum nigro- 

 venosum, studied by Schleip ('11), shows that the oogonial karyo- 

 somes form chromosomes while located in the nucleus centrally, 

 instead of peripherally, the position which is common in the 

 oogonia of most nematodes. Gulick ('11), working on Heterakis 

 \'esicularis, found that the heterochromosomes were notr dis- 

 tinguishable from the autosomes in the oogonia, but were in the 

 spermatogonia, coming from a separate karyosome, as they do 

 in A. canis Walton, '16 a). 



B. OOCYTES 



1 . First maturation division 



a. Prophase. The prophase extends through the period of the 

 'growth zone' of the sex cells; it is of long duration, as is shown 

 by the great number of cells with their chromosomes arranged 

 in the metaphase plate. The account which follows covers both 

 the nuclear and cytoplasmic conditions. 



The nuclear contents during this period undergo a very com- 

 plicated set of evolutions in the formation of the chromosomes 

 and in the preparation for the first maturation division. How- 

 ever, it is not possible to identify nearly as many stages as were 

 found in A. megalocephala by Saedeleer ('12), nor such details 

 of chromosome structure as those given by Bonne vie ('08) and 

 by Vejdovsky ('12) for the same species. Nevertheless, it is 

 possible to follow out the gross details of the 'method of the 

 formation of the chromosome tetrads and di-tetrads. 



The peripheral mass of chromatin noted after the last oogonial 

 division (fig. 4) breaks up (fig. 5) into a large plasmosome and 



