GENERATION. 



425 



liar change becomes an independent individual 

 entering upon a new life. Others arise like 

 the parts of a tree by buds which remain for 

 a time attached to the parent stem, and being 

 afterwards separated from it assume an inde- 

 pendent existence. A third class of animals 

 have the power of forming and throwing off 

 from their bodies a small portion of organized 

 matter, which, though at the time of its sepa- 

 ration from the parent, not resembling it either 

 in form or organization, is yet possessed of the 

 power of living for itselfj and, after passing 

 through a variety of successive changes of 

 growth and evolution, of at last acquiring the 

 exact semblance of the parent by which it was 

 produced. In a fourth and last class, com- 

 prehending much the greatest number of ani- 

 mals, the function of reproduction involves a 

 greater complication of vital processes than in 

 the three other classes above alluded to. The 

 union of two individuals of different sex be- 

 comes necessary, and the young owe their 

 origin to the evolution of a more complex 

 organized structure termed the egg, which is 

 formed in and separated from the body of the 

 female parent, and is the product of the union 

 of the male and female of all animals in which 

 the distinction of sex exists. The ovum or egg 

 is most familiarly known to us in the eggs of 

 domestic birds, to which the product of sexual 

 union in all animals belonging to this fourth 

 class bears a strict analogy in every essential 

 particular. 



It may be stated as a general fact, that the 

 reproductive function involves a greater num- 

 ber of vital processes in the higher and more 

 complicated than in the lower and simpler 

 kinds of animals. Yet there are exceptions 

 to this rule, and we do not always trace a 

 correspondence between the degree of com- 

 plication of the generative process of any 

 animal and the place which that animal holds 

 in the scale of being ; for there are some tribes 

 of animals which are propagated in more than 

 one of the ways above mentioned, and there 

 are some, to which, from the simplicity of their 

 other functions and organization, a low place 

 in the zoological scale has been assigned, and 

 which nevertheless resemble the higher animals 

 in respect to their mode of reproduction. 



A veiy superficial view, however, of the vari- 

 eties of the form obvious in the reproductive 

 process of different animals demonstrates the 

 importance of the reproductive functions in the 

 economy of life, as it points out the intimate 

 relation which these functions bear to the 

 habits, mode of life, and organization of each 

 animal, and shews the infinite care and fore- 

 sight with which nature, in every variety of 

 circumstance, has provided for the regular and 

 undisturbed performance of those acts by 

 which the species of organize I beings are con- 

 tinued from age to age, in an undeviating suc- 

 cession of generations. These facts also fully 

 justify our regarding, along with Cuvier, the 

 reproductive function as constituting one of 

 the fundamental divisions in a classification of 

 the processes of the animal economy. 



\\ hile, therefore, the principal object of the 



VOL. If. 



present article is to describe the process of 

 generation in Man and the higher Vertebrated 

 animals, it will be necessary and proper for us 

 to allude also to the reproductive function as 

 it is performed in all the various members of 

 the animal series; for in this, as in other de- 

 partments of Physiology, the more complicated 

 forms of the process derive much illustration 

 from the study of the more simple, and we 

 may hope thus more fully to point out the 

 general importance of the functions now under 

 consideration. 



We purpose to follow an arrangement 

 adapted chiefly to the consideration of Human 

 Generation. In all the animals in which dis- 

 tinction of sex subsists, the male and female 

 organs subservient to reproduction must co- 

 operate for the completion of the generative 

 process; and in the greater number of the more 

 perfect animals, as also in Man, the two kinds 

 of sexual organs being placed on separate in- 

 dividuals of the same species, the concurrence 

 of both these individuals, or of both male 

 and female parents, is necessary for the for- 

 mation of the fruitful products from which 

 the offspring proceeds. The circumstances, 

 then, which give rise to the union of the sexes, 

 and the phenomena which accompany that 

 union, form some of the topics of the present 

 article. The product of fruitful sexual union 

 in all animals is one or more eggs, from each of 

 which, under the influence of certain favourable 

 circumstances, different in different tribes, the 

 young animal is produced by an intricate pro- 

 cess of vital growth. The greater part of the 

 substance composing the egg is furnished by 

 the female parent : but this egg of the female 

 would be wholly barren, or would not undergo 

 any of those changes by which the young 

 animal is formed, unless it received in some 

 way or other the influence of the product of 

 the generative organs of the male ; and the egg 

 formed by the female may be regarded as im- 

 perfect until the change now alluded to has 

 been effected in it. It is then said to be 

 fecundated or rendered fruitful by the semen 

 of the male. The mode of formation of the 

 egg and seminal matter, the mode of their 

 separation from the place of their formation, 

 the structure and properties of each of these 

 products, the manner in which they are 

 brought together, the influence which they 

 exert upon one another, and the consequent 

 result in the production of the young, con- 

 stitute the principal remaining topics which 

 fall to be discussed by us at present. In this 

 article our attention must chiefly be confined 

 to such operations or functions of the male 

 and female parents as are preliminary to or 

 necessary for the formation of a ripe and fruit- 

 ful ovum, that is, an egg capable of giving 

 birth to a new animal the same as either of its 

 parents, when placed in those circumstances 

 which are favourable to its evolution. It is 

 not intended to speak in this place of the 

 changes of the ovum itself in which the for- 

 mation of the young animal consists : the 

 consideration of these is reserved for the article 

 Ovi M. 



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