198 INDIVIDUALITY OF CHROMOSOMES [CH. 



leptotene stage of the spermatocyte approaches, each of these 

 masses becomes resolved into a fine spiral filament ; at first 

 the spirals are distinct, but as they elongate they become 

 intertwined and soon give rise to a reticular appearance of 

 the whole nucleus. The threads of this apparent reticulum 

 then undergo a synaptic contraction, from which emerge 

 the pachytene threads that contract to form the spermato- 

 cyte chromosomes (Text-fig. 25). 



Although, therefore, the number of cases is not very large 

 in which the chromosomes have been traced through the 

 reticular or resting condition of the nucleus from one mi- 

 tosis to the next, this has been done quite definitely in 

 several animals and plants, and the results obtained give 

 strong indications that the d'fficulty of doing so in other 

 forms may not be due to the complete disappearance of 

 the chromosomes, but rather to their complicated inter- 

 lacing in the so-called reticular stage of the nucleus, for 

 which BOLLES LEE, on the basis of his observations on Paris, 

 proposes the name spirophase. And if the results obtained 

 in these cases are of general application, they suggest very 

 clearly that the individuality of the chromosomes does per- 

 sist in the resting nucleus. It is probable, however, that the 

 elongated filaments of the resting ("spirophase") stage are 

 not precisely equivalent to the chromosomes of the mitotic 

 figure, for as has been described in an earlier chapter, not 

 only does the absolute amount of chromatin in the nucleus, 

 as judged by its staining capacity, undergo considerable 

 fluctuations at different stages, but there is also strong 

 evidence that, in some cases at least, substance is withdrawn 

 from the nucleolus and converted into the chromatin of the 

 mitotic chromosomes. Several instances have also been 

 referred to of the emission of chromatin from the nucleus 

 into the cytoplasm. It would seem, therefore, that what 



