EMBRYOLOGY OF CRYPTOBRANCHUS 97 



area which is now visible in the hving egg. After remaining here 

 for a length of time that has not been accm^ately determined, the 

 germinal vesicle disappears from view leaving only a faint dark 

 spot to mark its former site. 



In most ovaries obtained about the time of the beginning of 

 the breeding season (the last week in August and the first week in 

 September), all stages in the emergence of the germinal vesicle 

 will be found; in some eggs the germinal vesicle has not yet 

 reached the surface, but in a considerable proportion of cases it 

 will be found exposed in varying degrees (see fig. 53) . 



The phenomena concerned with the appearance of the germinal 

 vesicle at the surface are very striking, owing to the large size 

 of the germinal vesicle, the sharp contrast between its transpar- 

 ent fluid contents and the surrounding opaque substance of the 

 egg, and the distinct appearance of several opaque-white bodies, 

 presumably nucleoli, within the germinal vesicle. All this may be 

 seen even with the naked eye. 



In order to obtain the sequence of the changes occurring in 

 a single egg during this stage, many individual eggs were isolated 

 in normal salt solution, or identified while in position in the ovary, 

 and kept under observation for several hours. In the case of the 

 first ovary studied during the fall of 1907, some of these eggs 

 changed sufficiently before death ensued, to enable me, by combin- 

 ing several individual histories, to get a fairly complete idea of the 

 normal course of events in a given egg. But in succeeding years, 

 although several dozen ovaries containing eggs in this stage have 

 been studied in females recently killed or anaesthetized with chlo- 

 retone, no marked changes could be detected. Hence in the 

 following account dependence is placed chiefly on a comparison 

 of individual eggs in the same freshly-exposed ovary, and a com- 

 parison of ovaries in slightly different stages of development.. In 

 particular, incipient stages in the approach of the germinal vesicle 

 to the surface could be distinguished from possible later stages in 

 which it has disappeared from view, through a comparison of 

 ovaries such as those described above, with others in which nearly 

 all the eggs had been set free from the ovary. 



