58 PETER OKKELBERG 



priate term, since apparently synapsis does not always occur 

 during this period. In the case of the lamprey it was not pos- 

 sible to find any pairing of the chromatin threads at this time, 

 although hundreds of cells were examined. 



Pachytene stage. In the pachytene stage (fig. 56), the chro- 

 matin material again becomes uniformly distributed throughout 

 the nucleus. It is now in the form of thick threads which appear 

 more or less continuous in some places, but are generally broken 

 up into segments. One large nucleolus appears. There is no 

 indication that the chromatin threads are paired. 



Diplotene-dictyate stage (diakinese) (figs. 57, 58, 59, 60, and 

 62). In an oocyte somewhat farther advanced than the above, 

 the whole chromatin network has become broken up into definite 

 chromosomes, and the paired structure of every chromosome is 

 very apparent, a condition which persists throughout the early 

 part of the growth period and probably up to the time of matura- 

 tion. It is very difficult, however, to follow the historj^ of the 

 chromosomes during the later growth period, since the nucleus 

 becomes very large and the chromatin material may be scattered 

 throughout its whole extent. The nucleolus at this time is large 

 and almost spherical. It has not been possible to observe any 

 relation between the nucleolus and the chromosomes at this 

 period of development. Many of the paired chromosomes lie 

 against the nuclear membrane, but they may occur also in vari- 

 ous other parts of the nucleus. Very often they are arranged 

 in the form of tetrads which are best seen along the nuclear mem- 

 brane (fig. 61). There appears to be no regularity in the arrange- 

 ment of the chromosomes. The dictyate stage (diakinese) con- 

 tinues during the growth period of the oocyte. 



Cytoplasmic changes. The nuclei of the oogonia are sur- 

 rounded by a small amount of granular cytoplasm. Often no 

 visible cell boundaries are present, although favorable sections 

 show that the cells do not form a syncytium, but are morpho- 

 logically independent of one another, in spite of the fact that no 

 true cell membrane is found. In cells, fixed in Meves' solution 

 or in other solutions that fix mitochondria, these occur in great 

 numbers. They are usually granular and appear to be more 



