of Human Monstrosity. 233 



appears at first as an aggregation of minute globules, which 

 arrange themselves on the inner surface of the exochorion. In 

 some one part they are accumulated in larger quantities so as to 

 represent a disc with a nucleus pointing towards the center of the 

 egg. From the interior of the yolk there proceeds a minute vesicle 

 containing a fluid. It moves towards the nucleus, penetrates it 

 and then bursts. The fluid diffuses itself amongst the globules 

 of the disc, which then assumes a membranous form, and is called 

 the cicatricula, the germinative membrane, or blastoderma of 

 Pander. The central vesicle is supposed to be the maternal por- 

 tion of the future germ, and when this process has taken place 

 the ovum is capable of impregnation. 



It was long doubted where the first appearance of the ovum 

 in mammalia could be ascertained. The observations of Cruick- 

 shanks, of Burns, of Prevost and Dumas, had sufficiently proved 

 that it may be perceived before its arrival in the uterus : for they 

 discovered it in the Fallopian tubes. But, since it had escaped 

 detection in the ovary, the ovarian vesicle of De Graaf in the 

 absence of any other ascertained rudiment, was considered to 

 afford the elementary fluid from which, at least in part it is 

 afterwards produced. At length by the more accurate observations 

 of Von Baer, the ovum itself was discovered within this vesicle. 

 It first appears as a collection of minute granules on the inner 

 surface of this vesicle, and is an aggregation of the globules of the 

 fluid. These globules themselves are not solid, but are vesicles of 

 a second order. Their investing portions coalesce to form a con- 

 taining membrane, whilst the fluid portions become the contents 

 of that membrane. 



The ovum presents singular varieties of size, in the different 

 orders of animals. In the dog it is in diameter not more than 

 Vol. IV. Part II. Go 



