THE OVUM. 291 



j'olk, contains the elements which are to undergo develop- 

 ment into the embryon. It is composed of a semifluid mass, 

 containing, in addition to the germinal vesicle, numerous 

 granules. Some of these granules are large, strongly-refract- 

 ing, globular bodies, which are so bright and so numerous, 

 that they obscure the other parts of the vitellus. Between 

 these, are numerous albuminoid granules, much smaller and 

 not so distinct. 



The germinal vesicle, sometimes called the vesicle of Pur- 

 kin je, 1 is the enlarged nucleus of the primordial ovum. 8 It 

 is a clear, globular vesicle, about -g-^ of an inch in diameter, 

 embedded in the vitellus, its position varying in different 

 ova. It presents in its interior a number of fine granules,' 

 and a large, dark spot, called the germinal spot, or the spot 

 of Wagner, 8 which measures about -g^Vfr of an inch in diam- 

 eter. This spot corresponds to the nucleolus of the primor- 

 dial ovum. In mammals, the mature ovum contains but one 

 germinal vesicle and one germinal spot. The observation of 

 Kolliker, who noted, as a rare exception, two vesicles in a 

 human ovum, has not been confirmed. 4 The various points 

 we have described are illustrated in Fig. 29. 



1 Purkinje (Symbolce ad Ovi Avium Historiam ante Incubationem, Lipsiae, 

 1830) was the first to describe this vesicle in the ova of birds. The original 

 work of Purkinje was not regularly published until 1830, having been first pre- 

 sented, in 1825, at a reunion to celebrate the fiftieth anniversary of the doctorate 

 of Blumenbach. Coste (Developpement des corps organises, Paris, 1847, tome i., 

 p. 115, et seq.} discovered this vesicle in the mammalian ovum, his first publication 

 bearing the date of 1834. In his large work, Coste seems to completely refute 

 the claims of Bernhardt and of_ Wharton Jones to the discovery of the germinal 

 vesicle in mammals. 



2 The ideas which have obtained within the last few years with regard to the 

 development of mature ova from simple cells, called primordial ova, were ad- 

 vanced by Robin, as early as 1862. (ROBIN, Memoire sur les phenomenes qui 

 se passent dans V ovule avant la segmentation du vitellus. Journal de la physiologie, 

 Paris, 1862, tome v., p. 67, et seq.) 



8 WAGNER, Prodromus Histories Generationis Hominis atque Animalium, Lip- 

 siae, 1836, p. 4. 



4 KOLLIKER, Elements d'histologie humaine, Paris, 1868, p. 705. 



