The form of the stomach in this Order of animals is perfectly simple, and does not greatly vary in the different genera. It is situated transversely with regard to the axis of the body, is somewhat elongated, and the two orifices are distant from each other, as in many of the Carnivora, and in the insectivorous bats. The cardiac pouch is generally distinct and rounded; the pyloric extremity, on the con trary, is conical and perfectly even. In Erina ceus the cardiac point is considerable, the en trance to the oesophagus being at no great dis tance from the pylorus - and the internal coat forms numerous rugw and folds. This form of the stomach and the existence of ph= must be considered as indicating an aberration from the insectivorous type, and a certain degree of ap titude for the digestion of vegetable matters, and we find accordingly that this, with a slight exception or two, is the only family of the Insectivora which can exist upon any but the most exclusive animal aliment. The mole, the Chrysochloris, and all their congeners, are in this latter case; but the hedgehog, as is well known, will readily eat various vegetable sub stances, and often digs under the common plantain for the purpose of obtaining the roots, of which it appears to be very fond. The sto mach varies a little in its form in the different genera of the Soricid&. In the great shrew of India it is transverse, the pyloric portion coni cal, of moderate dimensions, the cardiac pouch small and the two orifices distant; a form which indicates an exclusive aptitude for insect food; but it would appear that the water-shrews ( Ilydrosurex ) must occasionally have recourse to some kind of vegetable diet, as the pyloric portion is so much elongated as to resemble in some degree that of the or fruit eating Cheiroptera, exhibited in fig. 287, vol. i. p. GOO. In the mole the cesopliagus enters at about the middle of its anterior margin, and the lesser curvature is nearly straight to the pylorus. The membranes are extremely deli cate and almost transparent. The form is es sentially similar in Chrysochloris and in Con dyturu. The stomach of Tupaia, according to the Baron Cuvier, is of a globular form.
The intestinal canal is upon the whole re markably short in the Insectivora. There are some exceptions to this rule, but the only one hearing upon a difference of aliment is that of the hedgehog, which, as has been before ob served, lives partially upon vegetable matters. In this animal it is, with regard to the length of the body, as 6.6 to 1. In Talpa and Centenes this proportion is even exceeded, but it is com pensated for by the extreme narrowness of the canal ; the diameter of which is to its length, in the mole, as 1 to 82; whilst in the hedge hog it is as 1 to 58. In Sorex its length is to its diameter only as about 3 to 1, or a little more. There is no ccecum known to exist in any of the Insectivora. Cuvier queries whe ther Tupaia be not an exception, but this we have at present no means of ascertaining. The liver is in general fully developed in all its parts; there are the principal lobe, to which the gall-bladder is attached, with a notch answering to the suspensory ligament, a right and a left lobe, and two smaller lobes or lo buli, a right and a left. The whole of these parts are generally found, but varying without any known law, or any ascertained relation to functional peculiarity. In the hedgehog
and in the mole the left lobule is composed of two portions, a cardiac and a pyloric, as in the Rodentia. In Tupaia, according to the state ment of Cuvier, the three portions into which the liver is divided belong to the principal lobe; there is no right or left lobe, and the right lo bule is also wanting. The gall-bladder is for the most part of considerable size. In the hedgehog its fundus appears beyond the free margin of the liver, and is supported by a process of falciform ligament. In the Tenrec, on the contrary, it is as it were incrusted by the substance of the right portion of the prin cipal lobe.
IV. Nervous system.—The form and propor tions of the brain in some of the Insectivora ex hibit a degree of developement not materially superior to that of the higher Carnivora; whilst others, and especially the mole, have the same higher proportion which are found in the Chei roptera: thus in the hedgehog the volume of the brain is to that of the body as 1 to 168 ; whilst in the mole it is as 1 to 36. The pro portion of the cerebellum to the cerebrum in the latter animal, however, indicates a consi derable developement of the sexual functions, being as 1 to 4i. Supposing the theories of many modern physiologists to be correct, this fact is in perfect accordance with the neces sities of the animal, whose means of obtaining access to the opposite sex are extremely diffi cult, and require intense ardour and perseve rance to effect this object.
The most remarkable and interesting pecu liarities which are to be met with in the struc ture of any of the Mammalia are to be found in the eye of the mole, and doubtless of the nearly allied forms of Chrysochloris and the other subterranean species. In these, in order to meet the requirements of their habits, the organ of sight is reduced to a mere rudiment, whilst those of hearing and of smell are deve loped to an extraordinary degree ; and the theory of the balance of organs can scarcely boast of a stronger support in the whole range of animal organization than in this instance.
The question whether the mole possesses vi sion has been long and often debated. With out entering into an unnecessary examination of all that has been said on both sides of the question, it may be well to observe that the principal argument which has been urged on the negative is derived from the absence of an optic nerve. That this animal, at least our common species, does possess the faculty of vision to a certain degree cannot, however, be disproved, whatever may be the means by which the sense is communicated, that is to say, whatever the nerve may be which supplies the place of the true optic nerve ; and the ex periments of Henri le Court and Geoffroi St. Ililaire• would well nigh go to prove the affirmative of the proposition. It has been urged then that an optic nerve is absolutely necessary to the existence of vision; and that, therefore, either the mole has a true optic nerve, or that it does not possess vision. There have indeed been three classes of observers on this point ; those who maintain that the mole sees, and that it possesses an optic nerve ; those who contend that it is blind, and possesses no such nerve ; and others have ventured to agree with the former as to its power of vision, and with the latter in denying the existence of the optic nerve.