tint, each 3 grains in weight, and 8-10ths of an inch in length to the end of the tail: adhering strongly to the nipple, sucking actively, and clinging to the fur by the unguiculate digits of their fore-limbs, which they used freely. One survived separation from the nipple one hour and twenty-nine minutes, turned itself over and moved round the glass in various directions: respiring by the nostrils twenty-two times per minute, and ejecting bubbles of milk from mouth. The hind-limbs were each a mere bud, with feeble indications of toes, without claws. The tongue is very power of suction

large the entire weight of the head. The is such that the point of a pencil applied to the oral pore is held so strongly that the young can be partially lifted up by it. On March 14th the young weighed 12 grains, showing an increase of weight at the rate of 250 per cent. in seven days: it was now 1 inch long. On March 18th the weight was 18 grains: the claws appeared on the hind-toes: the testes had descended into a large scrotum. The eyelids were still sealed, but movements of the eyeball were visible beneath the skin. On May 22nd Dr. Meigs found one of the young crawling on the body of the dam; its weight was 42 grains; the eyes were open. This gave a term of marsupial gestation of 74 days. But the young return to the pouch for food and shelter until near the time for reception of a succeeding litter.

In Thylacinus the pouch opens backward, or vent-ward, as in Perameles; and shows four nipples. In a female which carried there three young, each 1 foot in length from the snout to the end of the tail, the length of the pouch was 8 inches; its aperture was 3 inches wide, and the bag expanded as it extended forward to a width of 6 inches. The teats were 4 inches long. The young were males: the testes had descended into a pendulous scrotum one inch in advance of the cloaca, from which the grooved but undivided penis projected: the eyelids were closed, but not adherent. The tongue presented a longitudinal rising, with a medial groove, the rising fitted into a depression on the roof of the mouth bounded by two, parallel, long and narrow palatal bones, recalling the condition of these bones in Sauria. In Myrmecobius the female is destitute of a pouch and has, apparently, eight nipples, arranged in a circle.' 2

Besides the natural and portable nest, some Marsupials (Didel phys, Phascogale, Charopus, Perameles) construct artificial ones. Perameles myosurus, e.g. makes a compact nest in a hollow of the ground, of grasses and other materials, which assimilate closely

CCLXXXI". p. 148.

2 CCLXXX". p. 394.

in colour and appearance to the surrounding herbage: " the nest is generally inhabited by the pair, with three or four young, when these are so large as to quit the pouch.

§ 415. In Lissencephala.-The fertile and commonly multiparous species of the Rodent order have corresponding provision for the nourishment of the young in the number of nipples. A seeming exception is presented by the domesticated breed of S. American Cavy, called Guinea-pig.' The prolific power of this well-fed pet is proverbial: they begin to breed at two months old, and gestation may be repeated at intervals of two or three months. The first litter consists of four, the second of five or six; and, as full maturity is gained by the mother, she may bring forth eight, ten, and even twelve young and yet she has only two nipples to serve them, turn and turn about. The teats are large and prominent, but lodged in a small shallow pouch, one on each side of the hind part of the belly. The mammary glands, however, attain a size more in accordance with the demands upon them they are not pendant, like an udder, but flat and spread over the abdomen. The wild original (Cavia aperea, Linn.) breeds but once a year, and then has but one or two young. Dolichotis has but two young. Echimys appears to have but two teats, placed midway between fore and hind legs: Rennger found two young in the nest at the bottom of the burrow: they were blind The Paca (Cologenys), with commonly two young, has four teats; and this number is not surpassed in Lagostomus, Cercolabes, Erithizon, Hystrix, Capromys, Helamys, Dipus, and some species of Sciurus (Sc. palmarum). In the Biscacha the anterior pair of teats is 1 inches behind the base of the forelegs: the posterior pair 2 inches farther back. In the prehensile Porcupine the hind nipple is midway between the fore and hind leg, the front nipple midway between this and the base of the fore-leg. Both these species, the common and the Canadian Porcupines, have usually two at a birth. The mother Coypu usually carries her young upon the back in her frequent traverses of the river she frequents: her teats are easily reached by the young so transported, as they project from the flanks, nearer the back than the belly the anterior pair are just behind the shoulders: the posterior pair anterior to the haunches. The nipples are rather less elevated than in the Coypu, in Hydrochærus, which swims with the young on her back: they are also lateral in Lagostomus, Octodon, Habrocoma, and Nelomys. In Octodon the foremost nipple is inch behind the base of the fore-leg: the hindmost pair are 2 CCLXXX". p. 299.

' CCLXXIX".

inguinal. In the burrowing Mole-rat the anterior nipple is on the inside of the base of the fore-leg, the posterior one at the middle of the inner side of the thigh. There are six teats in Bathyergus, eight in Loncheres, Octodon, and Dasyprocta, ten in Myoxus, and Lepus; twelve in the Rat and Mouse: even fourteen are said to have been noted in the Agouti, but this is probably abnormal. The Insectivorous order yields the maximum number of nipples in the mammalian class; as many as twenty-two having been observed in the tropical Hedgehog called Tenrec (Centetes), and the number rarely falls below fourteen. In such multiplication of teats and lacteal glands they extend along the under surface of the body from the pectoral to the inguinal region; and, in some Shrews (Sorex crassicaudatus, e.g.), the last pair of teats projects from the under side of the thick base of the tail. In the common Hedgehog (Erinaceus) there are ten teats, three pairs thoracic and two pairs abdominal, ranging from the pectoral to the inguinal regions. The thin and flat mammary glands seem to form a continuous stratum. In Shrews and Moles the teats are from six to eight in number. In the volant Insectivora they are usually reduced to two, and are pectoral in position, whence Linnæus was led to avail himself of this, with another outward genital character, to unite Bats in the same order (Primates) with Apes and Man. But the Sloths have one pair of pectoral teats and mammary glands. Many Armadillos, likewise, have two pectoral teats; to which, in a few kinds (D. novem-cinctus, e. g.), a pair of inguinal teats are added. The two-toed Anteater has two pectoral and two ventral teats. The great Anteater (Myrmecophaga jubata) is limited to two pectoral mammæ. The young animal remains with the mother for the space of a year, and is carried on her back. In a species of Phyllostoma I have seen two pubic as well as two pectoral teats. The latter in all bats are almost laterally placed, and in Pteropus are axillary: the nipple when in use becomes long, compressed, and sub-pedunculate. The Colugo (Galeopithecus volans) has two nipples in each arm-pit: they become large during maternity, for the young cling long to them.

Among Lissencephala the Rodents are most remarkable for nidificatory instincts. The little Harvest-mouse (Mus messorius) builds a round nest, like a Tit's, and attaches it, high up from the ground, to the stems of full grown rye, barley, or other cereal. The nest of the Marsh Hare (Lepus palustris) is formed of a large kind of rush (Juncus effusus), cut into pieces about a foot in length, and is arched over; the foundation of the nest is

usually a tussock surrounded by water, like a lake-dwelling: the number of young is from four to seven.

§ 416. In Mutilata.-In Cetacea the mammary glands, two in number, are oblong, narrow, flat bodies, lying between the dermal and abdominal muscles, with the subcutaneous blubber between them and the skin. The requisite mass of glandular substance at the suckling season is obtained by horizontal extent, not by thickness, so that they do not project, or interfere with the requisite shape of the natatory animal. Each gland has a principal duct running in the middle through the whole length of the gland, and collecting the smaller lateral ducts, which are made up of the still smaller ones. Some of these lateral branches enter the common trunk in the direction of the milk's passage, others in the contrary direction, especially those nearest to the termination of the trunk in the nipple. The trunk is large, and appears to serve as a reservoir for the milk:" it is continued from the hinder end of the gland, and terminates in a nipple concealed in a cleft, fig. 608, c, one on each side of the vulva, a, and toward the vent, b.

607

608

Position of mammary clefts, Porpoise.

CCLXXXIII".

The lateral portions of the cleft are composed of parts looser in texture than the common skin, which is probably to admit of the elongation or projection of the nipple. On the outside of this there is another small fissure, which gives greater facility to the movements of all these parts.

The nipple itself, shown by dilating the mammary fossa in fig. 607, is perforated by numerous lacteal ducts. Hunter thus alludes to the unusual circumstances under which the act of

1 XCIV. p. 392.

sucking must be performed in the present aquatic mammals:As either the mother or young one will be prevented from breathing at the time, their nostrils being in opposite directions, therefore the nose of one must be under water, and the time of sucking can only be between each respiration.' The considerable lacteal reservoir, and the quality of milk it contains,1 relate to this difficulty.

Some stress has been laid on the assistance which the muscles in contact with the mammary gland might afford by compressing the gland and ejecting the milk accumulated in the dilated receptacle; but,' as I remarked in CXLIV". p. 594, when we consider how great the pressure of the surrounding water must be upon the extended surface of the mammary gland, we may readily conceive that when the nipple is grasped by the mouth of the young, and the pressure removed from it by the retraction of the tongue, the milk will be expelled in a copious stream by means of the surrounding pressure alone, independently of muscular aid.'

season.

In Sirenia the mammary glands, also a pair, are pectoral in position; the teats are prominent and conspicuous at the suckling The mother has been seen holding her young to the breast, with one flipper, and maintaining both her own and her offspring's nostrils above water. The resemblance to a black woman and child has attracted attention, and the appearance of the tail-fin as she dived, has served to perpetuate the seaman's faith in the mermaid.'

§ 417. In Ungulata.-The Elephant resembles the Dugong in the number and position of the mammary glands and teats, which project between the fore-legs. The young animal compresses the gland with its proboscis as its sucks.

In the unimpregnated Rhinoceros the mammary glands, two in number, form a thin layer expanding forwards beneath the abdominal integument, between the dermal and abdominal muscles. The nipples are two in number and inguinal, are situated 14 inches in advance of the vulva, and 24 inches apart from one another. They are subcompressed, obtusely rounded at the extremity, and about 2 inches in length: about a dozen lactiferous ducts open upon the somewhat flattened summit of each nipple.

In the Mare and Ass the mammary glands, two in number, are situated between the thighs at a distance of about 9 inches in

The milk is probably very rich; for in that caught near Berkeley with its young one, the milk, which was tasted by Mr. Jenner, and Mr. Ludlow, surgeon, at Sodbury, was rich like cow's milk to which cream had been added.' XCIV. p. 392.