GERM-CELL HISTORY IN THE BROOK LAMPREY 57 



more advanced stage, but for a long time the chromatin remains 

 in a finely divided condition. The nucleus appears to grow 

 larger as the period progresses. The two nucleoli persist through- 

 out the period. 



Bouin ('01) studied this period in the oocyte of the frog, and 

 called the cells of this stage 'ovogonies de transition.' He de- 

 scribed the nucleus as losing its membrane at this time so that 

 there was a free communication between the nuclear and cyto- 

 plasmic substances. This has not been confirmed for other 

 forms and it is certainly not the case in t.he lamprey. 



Late leptotene stage. During this stage (figs. 53 and 54) the 

 chromatin network becomes much more distinct. The whole 

 nucleus is now filled with chromatin threads which cross one 

 another in various ways. Irregular thickenings are found on 

 the chromatin threads not only at their intersections, but in 

 other parts as well. 



Synaptene stage. During this stage (fig. 55) the chromatin 

 becomes massed together along one side of the nucleus in the form 

 of an irregular tangle of rather thick, deeply staining threads, and 

 forms what has been termed a 'contraction figure.' This is the 

 stage described by von Winiwarter as the synaptene stage and 

 by Marechal ('04) as the 'bouquet stage.' On the side of the 

 nucleus on which the chromatin is concentrated, the individual 

 threads can no longer be distinguished; but in the clearer parts 

 of the nucleus many of the ends of the chromatin threads extend 

 out from the concentrated mass, sometimes as far as the nuclear 

 membrane of the opposite side. Occasionally a nucleolus, which 

 later appears to be lost, occurs during the early phases of this 

 stage. It is possible that later, when it is not visible, it is hidden 

 among the chromatin threads of the contraction figure. If in 

 reality this be the case, it indicates a tendency of the chromatin 

 to concentrate around the nucleolus during this stage; for other- 

 wise, if the nucleolus be present, it should be found occasionally 

 in the clearer portions of the nucleus. Some investigators have 

 termed this period the synapsis stage, because in many forms the 

 chromatin threads come together in pairs at this time. McClung 

 ('05) has called it the 'synizesis stage,' and this is a more appro- 



