354 Dr, Paris on the Phi/siology of the Egg, [May, 



your notice, I shall briefly relate the successive operations by 

 which the egg is formed in the body of the animal ; the necessity 

 of more minute detail is superseded by the valuable descriptions 

 of Harvey and Malpighi. 



The rudiments of the ovum are first visible in the ovarium, 

 which, in fact, is nothing but a congeries ot vite/li* or yelks, 

 attached to the spine by a proper membrane ; this repository is 

 denominated by tabricius, the vilellariuni^ or vitel/onim raccmns, 

 and may be considered as analogous to the ovarium of the mam- 

 malia, or to the roe of fishes. These vitelli generally vary in 

 progression from the size of a millet seed to that of an acorn ; 

 each of which, according to its maturity, is successively 

 detached from the rest, whence it descends a tube, called, from 

 its resemblance to a funnel, infandibulumj and arrives at the 

 tUeruSy the internal surface of which is extended by spiral con- 

 "volutions ; here the albuminous fluids are secreted, and trans- 

 mitted to the vitellus during its passage to the finidus uteri, or 

 cloaca, where it receives its last addition, the external crust, or 

 ashell. 



The egg thus formed and completed possesses every essential 

 for its subsequent maturation, and requires only the emphatical 

 energy of heat for the developement of its embryon ; this is con- 

 veyed through different media in the different classes of animals. 

 In birds it is applied by incubation,t but in the amphibia and 

 other animals, the heat of whose bodies is inconsiderable and 

 inefficient, the eggs are deposited in mud or sand, or are 

 -exposed to the rays of the sun, by whose prohfic influence 

 myriads of beings are daily called into life and activity ; or they 

 are placed in other favourable situations, all of which are too 

 well known to the disciple of Linnaeus to require any particular 

 notice. It is, however, w^orthy of remark, that the medium 

 through which heat is applied is suitably varied in the same 

 species in diflerent climates. In Senegal, for instance, the 

 ostrich abandons her eggs to be hatched by the burning sands, 

 while in the more temperate and congenial regions of the Cape 

 of Good Hope, like other birds, she is inclined to incubation. 



The different species of ccstrjoi will afford us an illustration of 

 the variety of situations in which the insect tribe deposit their 

 ova; in which they are universally directed by an instinct to 

 ensure a suitable temperature, and appropriate nutriment for the 

 young brood ; thus the rcstrus hccmorrhoidaiis deposits them in 

 the rectum of the horse, and the jlL ovis in the frontal sinus of 

 ^heep, &c. 



♦ Vitellus, derived a vlta^ because it contains the embryon. 



f There are also other animals that accelerate the evolution of their ova by incuba- 

 tion. Thus bees in a hive generate a considerable quantity of heat witliout which their 

 eggs, would perish ; and the testudo mydait^ or common turtle, deposits her eggs in the 

 cand, and incubates during the night. i 



