424 



GENERATION. 



seminal glands, the latter embedded in the 

 erectile tissue of the corpus spongiosum. The 

 muscular portion does not always join the vas- 

 cular part in a straight line ; but, on the con- 

 trary, in some animals, as in Ruminants gene- 

 rally and in the Boar, the former opens by an 

 orifice perforated in the upper wall of the 

 latter, at a little distance from its commence- 

 ment, so that a cul-de-sac is left excavated in 

 the bulb of the urethra or commencement of 

 the spongy portion, in which the fluids poured 

 into the muscular part are mixed with the se- 

 cretion of Cowper's glands, which enters the 

 sides of the excavation. 



In Squirrels and Marmots a similar cul-de- 

 sac exists, which only receives the secretion of 

 Cowper's glands, arid is continued forwards 

 as a narrow tube surrounded by vascular tissue, 

 beneath the urethra, as far as the middle of the 

 penis, where the two canals unite. 



The course of the urethra in the great Kan- 

 garoo ( Macropus major) is peculiar ; instead 

 of passing, as is usually the case, beneath the 

 corpus cavernosum, it is inclosed in a canal 

 passing through the centre of the penis, from 

 which it only emerges at the extremity of the 

 glans ; owing to this arrangement, the spongy 

 investment of the canal is in this animal con- 

 founded with the vascular tissue of the corpus 

 cavernosum. 



In others of the Marsupiata the corpus spon- 

 giosum, like the cavernous body, arises by two 

 crura, which are quite unattached, each being 

 invested with a strong muscular sheath, and 

 even in some placental Mammals, as the Water- 

 rat and the Camel, rudiments of this division 

 are distinguishable. 



The glans penis, or extremity of the intro- 

 mittent organ, presents many modifications in 

 form and in the nature of its surface. It is 

 frequently smooth and highly sensible, as in 

 man, being only covered by a delicate skin ; 

 yet in other instances, as in the feline Carni- 

 vora, it is armed with stiff recurved bristles ; 

 sometimes the armature represents horny scales 

 or strong spines, and in not a few genera we 

 find horny serrated plates projecting from its 

 surface; and, as though these formidable saws 

 were insufficient, they are occasionally com- 

 bined with horny prongs protruded from the 

 extremity of the penis during its erection. 

 These last appendages are found in various 

 families of the Rodentia, as in Guinea-pigs 

 and Agoutis. The limits of this article will 

 not permit us to expatiate further on this part 

 of our subject; we must therefore refer the 

 reader for a description of the various forms of 

 the penis and of the muscles belonging to that 

 organ to the articles which treat of the Mam- 

 miferous orders individually. 



The female Mammalia exhibit in their gene- 

 rative system a beautiful gradation of struc- 

 ture. They naturally divide themselves in 

 conformity with their mode of gestation into 

 two classes, viz. the Ovo-vivipara or Marsu- 

 piata, and the Vivipara, properly so called, 

 comprising the placental orders. 



The former division approximates in every 

 particular to the oviparous type of structure : 



the ovaria are racemose, as in birds; the ovi- 

 ducts, which now assume the name of uteri, are 

 still double, opening by distinct orifices into 

 the vagina, which also is not unfrequently di- 

 vided. But the great feature which distin- 

 guishes the ovo-viviparous mammals is the 

 peculiar apparatus in which gestation is com 

 pleted, the embryo being expelled from the 

 uterus at a very early period, without ever con- 

 tracting any vascular connexion with that organ, 

 to be lodged in a marsupium or pouch con- 

 nected with the abdomen of the mother, in 

 which the nipples are contained. In this situ- 

 ation it becomes attached by its mouth to one 

 of the teats, and thus derives from the mam- 

 mary secretion the nourishment essential to its 

 growth. See MARSUPIATA. 



In the Placental division gestation is com- 

 pleted within the uterine cavity by the deve- 

 lopment of a vascular mass of different con- 

 struction in different classes, called the Pla- 

 centa. The ovaria here gradually lose their 

 racemose appearance, and are converted into 

 small and solid masses, in which the ova or 

 Graafian vesicles are evolved. The uterus, at 

 first completely divided, as in some of the 

 Rodentia, in which the two cornua open se- 

 parately into a single vaginal canal, by degrees 

 unites, and by a progressive coalescence attains 

 that concentration most perfectly exhibited in 

 the human female. 



To enter more largely into details connected 

 with the generative organs of the Mammiferous 

 classes would needlessly swell the bulk of this 

 article, in which our object has been to lay 

 before the reader a connected view of the mo- 

 difications met with in the reproductive system 

 throughout the animal kingdom, and thus to 

 connect with each other the numerous facts 

 relating to this subject which are elsewhere 

 more minutely recorded in this work. 



For the anatomy of the Organs of Generation in 

 Man, see PENIS, PROSTATE, TESTIS, VESICULJE 



SEMINALES. 



(T. Rymer Jones.) 



GENERATION (in Physiology) generatio; 

 Fr. generation; Germ. Zeugung; Ital. gene- 

 razione ;) is the process by which the young 

 of living bodies are produced, and their spe- 

 cies continued. In common language the 

 term is frequently confined to the mere act of 

 union of the sexes of animals ; but in general 

 and animal physiology it is generally employed 

 in the more extended signification given to it 

 in the following article, viz. to denote the assem- 

 blage of all the functions of animals concerned 

 in the formation of their young, and as syno- 

 nymous, therefore, with the function of Repro- 

 duction. 



In directing our attention to the mode in 

 which the function of reproduction is effected 

 in various classes of animals, so many striking 

 differences present themselves, that we find it 

 difficult if not impossible to point out any 

 general circumstances in respect to which they 

 all agree. Some animals, for example, are 

 propagated by the division of their whole 

 bodies into pieces, each of which by a pecu- 



