MAMMALS. 593 



and consists of two spongy bodies containing many blood-vessels 

 and a single spongy body which surrounds the urethra\ In many 

 marsupials a double gland is present^. In the feline genus tlie 

 glans is beset with horny spines ; in other mammals also, particu- 

 larly rodents, horny parts occur as plates or scales on this jiart. In 

 many mammals, the carnivores especially, there is found a small 

 bone in the gland, which is continued more or less into the tissue 

 of the penis. 



Milk-glands [mammce) exist in all mammals; they vary in 

 number and position ; in some, as the whales, they are placed in 

 the neighbourhood of the external sexual organs, but in all on the 

 inferior surface of the body. In the male sex they remain unde- 

 veloped, but in the female they secrete, especially for a longer or 

 shorter time after parturition, the milk which is the food of the 

 young. In the female of the duck-mole there is a large mammary 

 gland on each side consisting of long blind sacs, cellular internally ; 

 the efferent ducts open on a small, flat, oval space without any 

 nipple \ 



Impregnation is always effected in mammals by a real copula- 

 tion. One or more Graafian vesicles burst and the ovum, very 

 small in this class, escapes fi*om them; this discharge of the ovum 



GeneesJcunde, 1847, (and in V. Siebold u. Koelliker Zeitschr. f. w'lssensch. Zoologie, i. 

 1849, s. 295 — 346, Tab. 10, 21), and especially R. Leuckart in article Vesicula pro- 

 statica, Todd's Cyclop, iv. pp. 14 15 — 1429, who unites the opinion of H. Meckel (he 

 recognifsed in it a male vagina, Zur Morphologie der Ham- und GeschlecJds-werJczeuge 

 der Wirhelihiere, Halle, 1848, s. 48) with that of Weber, and considers the Weberian 

 organ to be a sinus genitalis, which in the female animal is developed into uterus and 

 vagina. To me the ojiinion of Meckel seems the most probable ; if the corpus uteri 

 and the vagina be derived from the Weberian organ, the corniM uteri still remain, and 

 the hypothesis, according to which the uterus arises from two different elements (a 

 vaginal portion and that of the horns proceeding from the two Fallopian tubes), is not 

 recommended by its simplicity. 



^ In dogs the spongy body of the urethra forms a tubercle at its anterior part 

 which swells on copulation ; see a figure in Panizza Osservazioni, Tab. i, copied by 

 Carus in his Tab. Anat. comp. ill. Fasc. V. Tab. 9, fig. 9. 



2 See a figure in Carus 1. 1. fig. 6. Compare on the male sexual organs of mam- 

 mals, besides the general works on comparative anatomy, F. Leydig in V. SlEBOLD 

 ti. Kolliker Zeitschr f. Wissensch. Zool. 11. 1850, s. i — 57. On the penis especially 

 Cuvier LeQons d'A^iat. comp., sec. ed. Tome viii. pp. 197 — 246. 



^ J. F. Meckel Ornitliorhynchi paradoxi descriptio anatnmica, Lipsiee, 1826, fol. 

 PP- 53) 54) Tab. viii. fig. 5 ; Owen Phil. Trans. 1832, and in Todd's Cyclop, in. 

 pp. 402 — 405. Tachyglossus presents a similar arrangement; see a small figure in 

 'Ba'rkow Zootomische Bemerhungen, Breslau, 1851, 4to, fig. 14. 



VOL. II. 38 



