No. 2.] THE DEVELOPMENT OF THE NEWT. 283 



germinal epithelium abutting on the germ-cell appear to accom- 

 pany the latter in its passage below the surface, and to become 

 its enveloping sheath. But I cannot regard these appearances 

 as conclusive and must still leave open the possibility of a late 

 "analysis" of one of the "primordial ova" into true follicle 

 and ovum. It is an hypothesis not altogether without warrant 

 that all the germinal epithelium cells may at the start be very 

 similar, or even identical, and that local conditions may bring 

 it about that some shall develop into ova and others into 

 follicle cells. 



Starting with the young ovum just sinking beneath the 

 surface of the other germinal epithelium cells we may con- 

 veniently separate its history into the two periods already 

 mentioned, the period of the accumulation of food-stuff, and 

 the period of the changes that qualify the female nucleus for 

 union with the sperm nucleus. The first period is marked by 

 the advent of new elements in the cytoplasm, and by rapid 

 increase in size of the ovum ; the second by the comparative 

 cessation of cytoplasmic phenomena, and by striking internal 

 changes in the germinal vesicle. 



The germinal vesicle in a young &g%, before any yolk 

 spherules are apparent, is about half the diameter of the egg 

 itself, measuring .07 mm. in an egg .13 mm. in diameter. Fig. 

 4 shows that in an even younger stage the germinal vesicle 

 occupies a slightly larger proportional share of the ^^g space. 

 The egg as a whole increases m size though not in complexity 

 up to a diameter of about .3 to .4 mm. when the first traces 

 of yolk begin to darken the field. (Fig. 7, Plate XV.) The 

 germinal vesicle up to this time has increased pari passu with 

 the whole Qg%, and in an ^gg of .4 mm. in diameter measures 

 .2 mm. From now on, however, while the yolk is grad.ually 

 forming, the growth of the whole &gg far outstrips that of the 

 nucleus. In an egg of 1.3 mm., which is very nearly the 

 average size of mature eggs, the germinal vesicle is only about 

 .3 to .4 mm. and rarely exceeds that proportion. In other 

 words the volume of the germinal vesicle compared with the 

 volume of the whole egg before yolk formation is about 1:8; 

 in the mature ^gg it does not exceed 1:35. 



