FEAIALE REPRODUCTIVE CELLS 



463 



appear to go through the various processes in groups which may be lik- 

 ened to the sperm columns of the testis. The cells are exceedingly small 

 during the early stages, so small that they can hardly be seen. They 

 are first recognizable as reproductive cells by the large black nucleolus, 

 and shortly after the outline of the expanding nucleus can be seen. When 

 they are between two and three microns in diameter, a cytoplasmic body 

 becomes apparent; the chromatin appears as a delicate spireme, and 

 they are ready to begin maturation (Fig. 429, og.}. No mitosis is ob- 

 servable which can be interpreted as an oogonial mitosis. 



The cells enlarge, and the chromatin becomes a delicate thread (Fig. 

 429, ogn.). It afterward grows stouter and gathers closely around the 

 nucleolus, which is of some size by this time. This is the beginning of 

 synizesis or the contraction stage, and presently the nucleus is completely 



, 430. Asterias Forbesii. Stages of the primary oocyte at early growth period. The nucleus 

 grows and yolk is accumulated. The chromatin thread breaks into chromosomes, which 

 become reduced in size. X 1500. (Drawn by H. E. JORDAN.) 



hidden by the crowding together of the chromatin masses (Fig. 429, 

 Syn.\ 



This stage does not last long, as is evidenced by the rarity with which 

 it occurs in any given section, notwithstanding the great number of ova 

 which are formed. More common are the stages which show the skein 

 of chromatin relaxed. The whole cell is very rapidly growing at this 

 time, and its size corresponds fairly well with the changes that, take place 

 in the chromatin. The skein or spireme enlarges with the widening 

 nucleus and becomes thicker. It is double, and its strands are granular. 

 Figure 430, A, shows this stage just as the spireme has begun to divide 

 into a number of pieces. The many small pieces shown in the figure 

 are largely the result of an artificial cutting and breaking of the chromatin 

 in the process of sectioning. 



In Figure 430, B, we see the portions of the chromatin spireme thick- 

 ened and shortened. They present, also, a mossy appearance at this 



