OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 539 



thirty-six small karyosomes or 'pro-chromosomes.' These bod- 

 ies become arranged near the periphery of the nucleus, while 

 the plasmosome assumes a more central position. At first these 

 'pro-chromosomes' are slightly ellipsoidal (fig. Q), but later 

 each becomes slightly constricted in a plane perpendicular to 

 its long axis, thus assuming a dumb-bell appearance (fig. 7). 

 Marcus ('06) interpreted this form of chromosome in another dog 

 ascaris as evidence of a reduction of the somatic number of 

 chromosomes by telosyndesis. 



The ovary has enlarged in cross-section faster than have the 

 oogonia. The latter, still in one layer around the rhachis, are 

 very loosely ])acked and the peduncle is readily apparent Hert- 

 wig ('90, taf. IV, fig. 7) figures a similar stage for the oocytes of 

 A. megalocephala. At the time of the appearance of the dyad- 

 like 'pro- hromosomes,' the nucleus has doubled in diameter, 

 while the cell body has increased its diameter by only one-fourth. 

 The plasmosome has now become almost central in position. 



The next stage in nuclear development follows quickly; it 

 shows a fine lin n network connecting together the peripheral 

 chromatic bodie;;, which now have lost their dyad appearance 

 and become more nearly cylindrical The plasmosome is sur- 

 rounded by this network, but is not connected with it (fig. 8). 

 To judge from its staining reactions, the plasmosome is non- 

 chromatic and not the source of the heterochromosome group. 



The network (fig. 9) now becomes more complex, and the 

 chromatic bodies, appearing as mere knots at the angles of the 

 network, are reduced in size. 



Following this stage, the network (fig. 10) becomes coarser 

 and the strands, much fewer become, very thick and jagged 

 in outline, varying greatly in diameter from place to place. 

 These network threads stain heavily in specific chromatin 

 dyes, showing that the chromatic material is distributed uni- 

 formly throughout the threads and not concentrated at their 

 junctions. The plasmosome is again peripheral and takes a 

 heavy stain, especially in Heidenhain's iron-haematoxylin. The 

 cytoplasm, while still retaining its finely granular or reticulate 

 condition, has begun to grow in size to keep pace with the growth 



