232 Professor Clark on a Case 



are formed, and of their early connexions with each other. And 

 once for all I refer below to those sufficient sources of infor- 

 mation*. 



An ovum is an organic production of a peculiar organ, the 

 ovary, in the form of a vesicle, containing a matter which through 

 a series of changes produces a new individual capable, when it has 

 reached a certain stage of its existence, of supporting an indepen- 

 dent life. Thus in all ova there are three parts, which are the 

 product of the ovary itself, viz. a nutrient matter, a membrane to 

 invest the whole, and an intermediate nucleus, or center, from 

 which the formation proceeds. 



The vitellus, or yolk, the earliest part of the egg, is an im- 

 mediate secretion from the ovary. It is contained in the membrane 

 of the ovum, which is smooth within and granular externally 

 and is called the cortical membrane, or exochorionf. Between 

 these two is gradually disposed the third part of the egg. This 



* Wolff. Uber die Bildung des Darmcanales, &c. mit Ammerkungen von J. F. Meckel 

 Halle, 1812. 



Purkinie. Symbol* a d ov i avium historiam ante incubationem. Vratislav, 1825. 



Pander. Diss, sistens Historiam Metamorphoseos quam ovum incubatum prioribus 

 quinque diebus subit. Wirceb, 1817- 



Dutrochet. Cuvier. Mem. du Museum, Vol. m. 1817- 



Geoffroy St. Hilaire. Monstruosites Humaines. Par. 1822. 



De Baer. De ovi Mammalium et hominum genesi. Lips. 1827. 



Entwickelungsgeschichte der Thiere. Kbnigsberg, 1824. 



Burdach Physiologic Leipsig, 1828. 



Serres. Prevost et Dumas. Annales des Sciences Nat. Vol. xi. xn. xvi. xxi. 1827 et 

 subseq. 



t Dutrochet applies this term to that part of the vascular membrane of the allantoTs 

 which is outward, when that sac is doubled over the embryo and its amnion. 



