SYNAPSIS IN THE EGG OF THE WHITE RAT 451 



THE NUCLEI OF THE EARLY GROWTH PERIOD 



By three days after birth, most of the nuclei have passed 

 over into the resting stage, so-called, and in this condition they 

 remain, with certain modifications, up to the period of sexual 

 maturity. Typically from one to three large definitely outlined 

 chromatin nucleoli are present. Throughout the remainder of 

 the nucleus a fine achromatic network is dispersed, with an 

 occasional deeply staining block or particle suspended mthin it 

 (text fig. 1). There is a decided increase in the size of the 

 nucleus coincident with the beginning of the enlargement of the 

 cell itself. The amount of achromatic material in these nuclei is 

 strikingly greater than that of any preceding period. Its ar- 

 rangement is without constant order and gives no hint of its 

 relation to the previous stages. If it be the linin of previous 

 stages, certainly there is here little evidence in support of that 

 theory which postulates that the individuality of the chromosome 

 is maintained through the constant discreteness of the linin 

 framework. 



THE CENTROSOME AND CHROMATOID BODY 



While no attempt has been made to analyze carefully the 

 cytoplasmic changes which occur simultaneously with the series 

 of nuclear alterations just described, our attention has been 

 drawn to two distinct structures which appear in the cytoplasm 

 very constantly during a part of the process. These are the 

 so-called centrosome or body of Balbiani and the chromatoid 

 bodies. The centrosome appears as a roughly spherical or elon- 

 gated condensed portion of finer texture than the remainder of 

 the cytoplasm, lying never more than half way from the nuclear 

 wall to the periphery of the cell. It has no definite mem- 

 brane and its outline is uneven. It is first discernible in the 

 early leptotene nuclei (fig. 9) where it may occur in only a 

 comparatively small percentage of the cells. Throughout the 

 synaptene stage it is more conspicuous, and only rarely at this 

 time is there within it a darkly staining granule, perhaps the 

 centriole. It is very evident in most of the cells in the pachy- 



