OOGENESIS AND EARLY EMBRYOLOGY ASCARIS 549 



reactions and by its behavior, the plasmosome is entirely achro- 

 matic in nature, and is not a storehouse for either chromatin in 

 general (Marcus, '06), or the chromatin of the heterochromo- 

 somes (Medes, '05; Boring, '07; Dederer, '07; Randolph, '08; 

 Stephens, '08, '10; Payne, '09; and Goldsmith, '16). 



Following the formation of the di-tetrads (figs. 23 and 24), 

 the autosomes lose their peripheral position and mix with the 

 already centrally located members of the heterochromosome 

 group, from which they cannot now be distinguished. 



After the most careful study of this and closely related stages, 

 the writer has failed to see any sign of a centrosome system. 

 Such a structure is first noted when there are two centrosomal 

 bodies which have taken up their positions at the opposite poles 

 of the nucleus. A cell of this stage is shown in figure 26 with 

 the fundaments of the maturation spindle in process of forming, 

 and the nuclear walls already' breaking down at its poles. 

 Whether this apparent absence of the early stages of the centro- 

 some is due to an inherent inability to take stains, or to gaps in 

 my material, has not as yet been determined. Coincident with 

 the setting up of the maturation spindle, the chromosomes gather 

 into the equatorial region of the nucleus (fig. 26) to form the 

 metaphase plate (fig. 27) in preparation for the first maturation 

 division. 



During these nuclear changes the cytoplasm has become much 

 vacuolated. The majority of the larger vacuoles are arranged 

 near the periphery of the cell. The alveolar nature of the cyto- 

 plasm can be clearly seen, but the alveoli apparently do not 

 tend to form rows radiating from each centrosome, — by which 

 the astral figures are emphasized, — as they do in the correspond- 

 ing stage of the spermatocytes (Walton, '16 a). The cell wall is 

 still exceedingly thin, appearing in sections as a very faint line. 



b. Metaphase. A very noticeable change of achromatic, as 

 well as of chromatic, material is noted in the early metaphase. 

 The cell wall thickens and appears to be of a structureless, jelly- 

 like nature (fig. 27). The cytoplasm immediately surrounding 

 the centrosomes has lost its alveolar structure, leaving them 

 imbedded in a small sphere of undifferentiated material. There 



