■;oo JORDAN. [Vol. VIII. 



o 



stainability, and stain more and more feebly until it is only 

 with the closest scrutiny that they can be observed at all 

 (Fig. 1 6). This fact, I think, accounts for the overlooking of 

 these structures by Schultze. The apparent feeble reaction of 

 the older chromosomes to stains may be due either to chemical 

 change in the chromatic substance or to the mechanical 

 separation of the chromatin granules. About the time that 

 the nucleoli break up, the chromosomes become more deeply 

 stained ; whether this indicates a welding together of the 

 chromosome substance or a different molecular constitution 

 I must regard as an open question. The problem of the 

 number of chromosomes at different stages in the history 

 of the ovarian 0,2,^, which has been raised by the interesting 

 researches of Ruckert ('92) on Selachians, may safely be left 

 until the actual existence of independent elements is definitively 

 demonstrated. 



General cojisideratioiis. — The history of the germinal vesicle 

 and its parts, as thus far outlined, brings us to an estimate 

 of the general significance of the phenomena observed. 

 It is a time-honored hypothesis that the substance of the 

 egg-cell of ev«ry organism is differentiated into two radically 

 unlike protoplasmic parts, into a part concerned wholly with 

 the transmission of hereditary qualities, and a part occupied 

 solely with the development of the egg-cell. The principal 

 bearer of the hereditary tendencies is considered by many 

 to be the nuclear chromatin network, composed of the so- 

 called Idants of Weismann, which are handed down from 

 generation to generation practically unchanged by somatic 

 influences. 



There is not this consensus of opinion, however, regarding 

 the seat of the ovogenetic or histogenetic element. This 

 ovogenetic element has been variously regarded as resident in 

 the yolk-nuclei, as an attribute of the cytoplasm itself and as 

 inextricably mingled with the germ plasm. The now abandoned 

 hypothesis according to which the ovogenetic substance was 

 thought to be sundered from close association with the germ 

 plasm and then expelled as the first polar globule is too familiar 

 to need comment. A more recent view is that put forth by 



