GENERATION. 



445 



like other laws of the reproductive function, is 

 subject to some modification, and we find ac- 

 cordingly several allied species of the domestic 

 animals breeding freely together ; and there are 

 not wanting, even in the wild state, examples 

 of the mixture of distinct species. 



The animal produced by the union of the 

 male and female of distinct species receives 

 the name of Hybrid or Mule, which generally 

 partakes of the qualities of both its parents in 

 a greater or less degree. Here again we find 

 another effectual impediment put by nature to 

 the mixture of different species, in this circum- 

 stance, that the mule, whether male or female, 

 is usually unfit for propagation. The offspring 

 of male and female of distinct species is much 

 more frequently fruitful than that of distinct 

 genera.* The instances of the former are not 

 few, as in the wild and tame cat, the wild 

 boar and domestic hog, the pheasant and 

 domestic fowl, the wild and tame duck. 

 But the instances of the latter or mixture of 

 distinct genera are very rare, and most of them 

 require confirmation. We must at the same 

 time always hold in mind that the distinction of 

 species by naturalists is at all times artificial or 

 made by man, how much soever he may con- 

 ceive his classification to be founded in nature, 

 and those animals which are regarded by one 

 naturalist as different species of the same 

 genus are made by others to constitute distinct 

 genera. 



It is well known that in gardens and else- 

 where, although the pollen of very various 

 plants is almost constantly flying about through 

 the air, it is only among the most nearly allied 

 races or varieties that mixture occurs, and the 

 instances of the mixture of different species of 

 plants are very rare indeed. Many of the 

 mixed varieties so produced cannot be pro- 

 pagated by seeds ; so that there is in the vege- 

 table as well as in the animal kingdom a con- 

 stant tendency to return to the original distinct 

 species. 



The milt and spawn of different fishes are at 



* The following examples of the mixture of 

 species are given by Burdach, but some of them 

 require confirmation. 



Papilio Jurtina unites with P. Jurtina. 



Chrysomela JEnea. ,, C. AIni. 



PhalangiumCornutum P. Opulio. 



Cyprinus Carpio 



Fringilla Carduelis 



Phasianus Callus 



Anas Olor 



Anas Glaucion 



Tetrao Tetrix. 



Corvus Corone 



Canis Familiaris 



Canis Familiaris 



Equus Caballns 



Equus Cabal lus 

 Equus Zebra 

 Equus Caballus 

 Capra Hircus 



Raua 



Tetrao Tetrix 

 Capra Hircus 

 Cervus Elaphus 

 Ce*vus Elapus 



C. CarassiusorGxbelip. 



F. Canaria. 



P. Colchicus. 



A. Anser. 



A. Querquedula. 



T. Urogal'.us. 



C. Comix. 



C. Lupus. 



C.Vnlpes. 



E. Zebra. 



E. Asinus, 



E. Asinus. 



E. Quagga. 



C. Ibex. 



The examples of gen ra breeding together are 

 much less numerous. 



Bufo. 



Phasianus Colchicns. 



Antilopc Rupicapra. 

 Bos Taurus ? 

 Ovis Aries. 



the same time floating in the same water, but 

 even thus brought into close union with one 

 another, no mixture happens. The ingenious 

 experiments of the celebrated Spallanzani, 

 who attempted to impregnate artificially the 

 ova of one animal with the seminal fluid 

 of another, and the unsuccessful attempts of 

 many to cause different animals to breed toge- 

 ther, afford still farther proofs, were they want- 

 ing, of the number and completeness of the 

 impediments which nature has opposed to the 

 promiscuous breeding of distinct species. 



The horse and ass are caused, it is known, 

 to unite by man, and do not naturally do so; 

 and in the wild suite it is probable that the 

 exceptions to the general rule before-mentioned 

 occur only when the male is deprived of his 

 natural female. It seems scarcely necessary 

 to state that the stories of fruitful union of 

 either male or female of the human species 

 with apes or other animals, considered as au- 

 thentic by some authors, are entirely fabu- 

 lous. 



In a subsequent part of this article we shall 

 have occasion to revert to the subject of the 

 mixture of races in our remarks upon the 

 transmission of the qualities of the parent to 

 the offspring. 



6. Functions of the external organs of re- 

 production. In addition to sexual feelings, 

 the state of turgescence or erection of the ex- 

 ternal organs by which copulation is effected, 

 is a more or less constant antecedent and 

 concomitant of the first act of the generative 

 process. This condition belongs more pro- 

 perly to the external sexual organs of the male, 

 and especially the penis ; but it also frequently 

 exists in some parts of the female organs. 



The erection of the penis producing the 

 rigidity of that organ necessary to ensure eja- 

 culation or forcible emission of the seminal 

 fluid, consists essentially in the increased 

 quantity of fluid in its bloodvessels, and is 

 with most reason to be attributed chiefly to the 

 peculiar structure and inherent properties of 

 the tissue, so called erectile, of which it is. 

 mainly formed. The manner in which the- 

 greater accumulation of blood in the erectile 

 tissue is brought about is by no means suf- 

 ficiently clearly expkined, Two different 

 opinions prevail as to the cause of this phe- 

 nomenon ; the one> that the flow of blood is 

 retarded in the veins by the contraction and, 

 consequent pressure of certain muscles situ*- 

 ated towards the root of the penis the other, 

 that the turgescence of erection is caused by 

 an altered action or condition of the blood- 

 vessels themselves, peculiar to the erectile 

 tissue, in which they are capable of admitting 

 and retaining a greater quantity of blood in 

 the erected than in the collapsed state. 



We must refer to the various anatomical 

 articles for an account of the structure of the 

 erectile tissue and the organs in which it occurs.; 

 we shall in this place advert to those points 

 only which seem to bear upon the physiological 

 view of their function. 



The glans penis, corpus spongiosum urethra, 

 and. corpora cavernosa penis, consist in great 



