Chap. II. AURELIA FLAVIDULA. 13 



With a magnifj'ing power of two hundred diameters we have seen simple 

 gloljular bodies (PI. X". Figs. IG and 17) scattered among the cells of the ovary, 

 but did not ascertain whether they were the discharged mesoblasts of the neighboring 

 tissue, or started from much smaller bodies than were then seen. That these are 

 eggs is proved by eas}^ and direct observation; for, starting here, we may trace a 

 gradated series of similar bodies, of intermediate sizes {Figs. 16, IT, 18, 19, and 20), 

 between the smallest and those which have all the characteristics of a genuine egg 

 {Fi(J. 21). The smallest of these httle globular bodies {Fic/s. 16, 17, and 18) resemble 

 spheres of jelly, perfectly homogeneous throughout. When, under the same magni- 

 fjdng power, the egg appears to the eye to be about one eighth of an inch in 

 diameter {Fig. 19), its contents consist of comparatively large globules, five of which 

 would occupy the whole diameter of the egg. These globules are perfectly clear 

 and homogeneous, and very remai'kalale, from the fact that so few yolk granules should 

 fill a whole egg. They do not seem to Ije permanent, for in another egg {Fig. 20), 

 not much larger than this, the globules are considerably smaller and much more 

 numei'ous. The intermediate state between these two eggs we have not seen ; but 

 there can hardly be any doubt that there is a total breaking up of the globules of 

 the first egg, and then a new development, in order to produce the smaller globules 

 of the second.- It can hardly be supposed that these extensive changes could go on 

 in such a body without being limited by a definite envelope having sufficient con- 

 sistency to resist the breaking out of the unstable contents ; yet such would seem to 

 be the fact at first sight. But when we examine more closely we find, that although 

 it is difficult to detect any definite boundary short of the superficies of the egg, 

 yet it is palpably evident that the globular contents of the first egg {Fig. 19) are 

 restrained Avithin an area which has its limits at a very marked distance within 

 the peripher}^ Here it would seem, then, that the vitelline sac has the same 

 degree of refraction as the fluid portion of the yolk, l:)ut possesses a greater degree 

 of consistency, and perhaps a different density. This fact should be borne in mind 

 by those who advocate the formation of the Purkinjean vesicle as a primary step 

 in the development of the egg, and the subsequent deposit of yolk around this 

 vesicle as a nucleus, previous to the development of the yolk-sac. 



By the time the egg has grown to be one third greater in diameter {Fig. 21) 

 than the last one {Fig. 20) mentioned, the Purkinjean vesicle {Fig. 21 1^) has appeared, 

 and developed to a considerable size, in fact fills one half of the diameter of the 

 egg, and the Wagnerian vesicle {w) already occupies one foiu^th of the diameter of 

 the Purkinjean vesicle. Both these vesicles are perfectly clear and homogeneous. 

 The 3'olk-cells are no larger than in the last phase, but more densely packed; so 

 that their cellular nature is not so easily recognized, and therefore they appear more 

 like a mass of granules, as represented in the figure. If the egg were magnified 



