60 PETER OKKELBERG 



much like those of the female. In both sexes the germ cells 

 presumably come out of the synaptic phase with the nmnber of 

 chromosomes reduced to one-half the number found in the pre- 

 synaptic cells. The subsequent history of the cells, however, 

 differs in the two sexes. In the female the cells grow to an enor- 

 mous size by the accumulation of yolk, while in the male there is 

 very little growth. 



Aside from the apparent pairing of the chromosomes during 

 the period of multiplication, no other instance of chromosome 

 pairing was observed in the cells before they have reached the 

 diplotene stage; but it cannot be said with certainty that a doub- 

 ling does not take place before this stage during the synaptic 

 phase. In some forms which have been investigated, synapsis 

 seems to take place during the synaptene stage, or during the 

 period of transition from the leptotene to the synaptene. Von 

 Winiwarter ('01) figures a pairing of the chromatin threads in 

 the germ cells of the rabbit during the early synaptene. Von 

 Winiwarter and Sainmont ('09) describe a similar condition in the 

 cat. In Proteus also, according to Jorgensen ('10) the leptotene 

 stage is followed by a stage which shows a double nature of the 

 chromatin threads. In Bufo, King ('08) figures double chroma- 

 tin threads for the first time after the synaptene stage. Marechal 

 ('04) observed the double structure of the threads during the 

 synaptene stage in Pristiurus and Scyllium and later ('07), in 

 Ciona and Amphioxus. Janssens ('04) found that in Triton the 

 reduced number of chromosomes, or chromatin filaments, appears 

 shortly after synizesis and that these filaments subsequently 

 split longitudinally forming two sister threads which remain 

 together. d'Hollander ('04) found a massing of chromatin 

 (synizesis) in the oocyte of the hen before synapsis. 



The phenomenon of synizesis (McClung, '05) has been found 

 by various investigators to occur in the oocyte of invertebrates 

 as well as in vertebrates; it seems to be a universal phenomenon 

 of the early heterotypic prophase. Chubb ('06) thinks that 

 synapsis takes place in Antedon during the oogonial divisions, 

 and that it is followed by still one more division. In Sycon 

 Jorgensen ('10) thinks that the reduced number is present in 



