536 A. C. WALTON 



plasm contains very finely granular matter scattered uniformly 

 throughout its substance. 



The division of the nucleus is clearly by the indirect method, 

 although the chromatin, as in the spermatogonia, appears as a 

 single mass, instead of being resolved into individual chromo- 

 somes. From this chromatin mass a nuclear plate is formed 

 (fig. 2) in the equatorial plane of the spindle. Traces of the spin- 

 dle are likewise to be seen; but the actual centrosomes cannot 

 always be made out, owing to the extreme smallness of the ele- 

 ments involved. This nuclear plate divides into two equal, 

 somewhat saucer-shaped bodies (fig. 3), which migrate, one to 

 each pole of the spindle. Cell division follows immediately, 

 the solid chromatin mass of each daughter cell occupying a 

 peripheral position in the reconstructed nucleus (fig. 4). This 

 daughter plate later moves to the center of the nucleus in all ex- 

 cept the daughter cells of the last division. In the latter (fig. 5) 

 it becomes differentiated into its component chromosomes while 

 still occupying a peripheral situation. A large, intensely stain- 

 ing body (the plasmosome) also emerges from the common 

 mass of material found in the earlier stages. Marcus ('06) 

 found that the plasmosome in the dog ascarid (A. canis?) studied 

 by him originated in the same way. 



To judge from its staining reactions, this certainly corresponds 

 to the plasmosome of the spermatogonial cells, not to the smaller 

 of the two karyosomes, which in the male, as has been shown 

 (Walton, '16 a), is made up of the heterochromosome group. 

 The ' 2X' character of the female is not shown by a distribution 

 of the chromosomes into separate karyosomes, as is the case in 

 the male sex cells (Walton, '16 a, plate 1, fig. 1). 



This formation of definite chromosomes and a plasmosome is 

 recognized only after the last of the numerous oogonial divisions, 

 which marks the end of the 'multiplication' of cells, this zone 

 extending through one-eighth of the total length of the ovary. 

 During this period the cytoplasm maintains its characteristic 

 granular appearance with very slight, if any, indication of a 

 fibrillar or alveolar structure. 



Owing to the minuteness of the cells at this stage, very little 



