218 First Alaluratiuu SpiiulJo of Allolubopliora Fcotida 



tivcly achromatic and chromatic segregation which appears hiter. Plioto. 

 Ill, Plate yil, shows an early stage of the segregation of the diffused 

 chromatin into a delicate thread or threads which later form the pro- 

 nounced spireme of Photo. 113. At this early stage of the spireme the 

 entire germinal vesicle is traversed hy a delicate thread so closely entwined 

 that it gives the appearance of a network and it has heen impossible to 

 determine whether this is composed of one continuous thread. Photo. 

 Ill represents a typical distribution of the chromatin at this stage. "We 

 have a large number of similar preparations and many photographs, l3ut 

 lack of space prevents our reproducing more than one. 



Photo. 112, Plate A^II, shows a very different segregation of the chro- 

 matin, the chromatic granules of the nucleoplasm are collecting directly 

 into a coil-like structure without passing through the stage shown in 

 Photo. 111. We have only one such preparation and we interpret it as 

 abnormal, but ha\'e reproduced it because it shows so clearly that the 

 chromatin is distributed throughout the entire germinal vesicle, and be- 

 cause that part of the nucleoplasm which is not 3'et differentiated into 

 chromatin and achromatin gives a very faithful picture of the entire 

 nucleoplasm of oocytes in an earlier stage of development. The granular 

 nucleoplasm as shown on the right periphery of the germinal vesicle of 

 Photo. 112 gradually segregates (in normal eggs) into an extremely deli- 

 cate chromatic network, which is at first as indistinct as that shown at 

 the left side of the germinal vesicle of Photo. 111. 



Photo. 113, Plate VII, is a germinal vesicle showing a typical early 

 stage of the spireme. A study of this photograph in the light of Photo. 

 Ill suggests that the spireme of Photo. 113 has been formed by a con- 

 traction and thickening of the delicate thread or threads of Photo. Ill 

 or by the fusing of parallel strands. 



A study of Plioto. 11-i in the light of Photo. 113, Plate VII, suggests 

 that each part of the double thread of Photo. 114 may be the single thread 

 of Photo. 113, or, as we are inclined to think, that the single thread has 

 increased in thickness by contraction and growth and has subsequently 

 split. The longitudinal split of the spireme seen in Photos. 11-t and 115 

 persists throughout the prophase and can be clearly seen in many of the 

 chromosomes at the metaphase (cf. Plates VIII and IX). "We interpret 

 Photos. 114 and 115 as a later stage than Photo. 113 because the thread 

 has commenced to break apart transversely to form the eleven bivalent 

 chromosomes. 



In Photo. 116, Plate VII, the entire spireme has divided into bivalent 

 chromosomes with the exception of the two bivalent chromosomes which 

 are close to the accessory nucleolus. These are still attached end to end. 



