452 OF GENERATION AND DEVELOPMENT. 



rection of both movements being the same, namely, from the ovaries 

 towards the uterus. If in their course they should not receive the fer- 

 tilizing influence, they appear soon to die and to disintegrate ; but if they 

 should be impregnated by contact with the spermatic fluid, they almost 

 immediately begin to undergo the first of those changes, which tend to 

 the production of a new organism. 



803. Much discussion has taken place, with regard to the exact point 

 at which the fertilization of the ovulum takes place ; but this does not 

 seem to be a matter of much consequence, as we find the order of the diffe- 

 rent steps to vary considerably in different classes of animals. Thus in 

 many aquatic Mollusca, and even in a large proportion of the class of 

 Fishes, there is no act of copulation whatever ; but the spermatic fluid, 

 when emitted by the male, is diffused through the water, and fertilizes the 

 ova which have been deposited by the female in his neighbourhood. In the 

 Frog, again, and in other Reptiles, the spermatic fluid is emitted upon 

 the ova, at the time that they are being extruded by the female. In 

 many Insects and Crustacea, in which a single congress often serves to 

 fertilize many thousand eggs, the deposition of which occupies a period 

 of several weeks or months, the spermatic fluid is received and stored 

 up in a saccular dilatation of the oviduct of the female, which is termed 

 the spermo-theca; and in this manner it serves to impregnate the ova, as 

 they are successively developed, and are conveyed to the outlet of the 

 oviduct. In Birds, we find that ova are often set free from the ovarium 

 in a state of full maturity, but without fertilization ; and that they re- 

 ceive their additional layer of albumen and their shelly envelope, in 

 passing down the oviduct, so as, at the time of their deposition, to differ 

 in no obvious particular from fertile eggs. It is doubtful, in regard to 

 Mammalia, whether the act of fertilization takes place before the ovum 

 has been completely extricated from the ovisac, or subsequently to its 

 finally quitting the ovarium and being received into the Fallopian tube. 

 It is quite certain that the spermatozoa frequently, if not invariably, 

 find their way to the surface of the ovary, being carried thither by 

 their own spontaneous movements ; and it seems on the whole most pro- 

 bable, that the fertilization of the ova usually takes place before they 

 have entirely escaped from the ovisac, or whilst they are still in the 

 commencement of the Fallopian tube. It is not unlikely that the place of 

 the act of fecundation varies, according to the point at which the ovule 

 and the seminal fluid first come into contact, which may depend upon 

 the degree of maturity of the ova at the period of copulation. 



804. Everything indicates that the contact of the Spermatozoon with 

 the Ovulum is the one thing needful in the act of fecundation ; and there 

 is strong reason to believe, from Mr. Newport's recent observations, that 

 when this contact occurs, the spermatozoa undergo solution ; and that it 

 is in the absorption of the product of that solution into the interior of 

 the ovum (thus blending, as in Plants, the contents of the "sperm-cell" 

 with^ those of the " germ-cell"), that the act of fecundation essentially 

 consists. Availing himself of the agency of caustic potass, which has 

 been, found to be a powerful solvent of the spermatozoa, Mr. N. applied 

 this agent to the ova at determinate periods after the application of 

 these bodies, which he had separated from the liquor seminis by filtra- 



