thoracic duct has been observed, with a similar arrangement, in the Dog and Sea-otter. In most Carnivora the mesenteric glands are aggregated in one mass, known to the old anatomists as the pancreas Asellii:' in the Weasel it is in two masses, and in the Cat, Ichneumon, and Seal has been found more subdivided. In these, however, there is one principal gland or vasoganglion,' the efferent vessels of which quickly unite into a trunk grooving its dorsal surface in the Seal, from which two main canals proceed to the thorax. In Ungulata and Quadrumana the mesenteric glands are numerous. I have noticed a large one in the mesocolon of the Echidna, near the rectum. The chyle-receptacle is large and cavernous, sometimes bilocular, in the Horse: the thoracic duct has shown varieties like those above described in Man, but it always terminates in the precaval vein at the union therewith of the two jugulars. In the Ox the lymphatic trunk perforates the diaphragm by an aperture distinct from that of the aorta it usually bifurcates, sometimes becomes plexiform, in the thorax: the two divisions diverging to the right and left innominate veins formed by the junction of the jugulars and axillaries. In the Hog the thoracic duct has been observed to terminate in the azygos vein. The orifice of communication with the venous system is usually defended by a pair of semilunar valves; but varieties have been noted, and, after death, blood has been observed in the thoracic duct of the Horse. Independent movements of contraction and dilatation have been witnessed in the chyle-receptacle and lacteals of the Ox;1 but no rhythmically pulsating sacs have been detected in the absorbent system of Mammalia, nor have other points of communication with the venous system been uncontrovertibly determined, save those above described. 1 CLXXV'. CHAPTER XXXII. CIRCULATING SYSTEM OF MAMMALIA. § 346. Blood of Mammals. The blood in this class is hot and red, with a proportion of organic matters to the water as great as in Birds, and more abounding in blood-discs, which, as a rule, are of a circular form, and of smaller size than in Ovipara, consisting of viscous hematosine without a cell-wall (vol. i. fig. 8, a, b). Besides the ordinary red discs there occur pale or granulated vesicles, the appearances of which, in the blood of a Perameles examined by me in 1838, 'suggested the idea that such blooddisc was undergoing a spontaneous subdivision into smaller vesicles.'1 The existence of a capsule, or rather a difference between the peripheral and central parts, in ordinary mammalian blood-discs, seems to be demonstrated by submitting them to a solution of magenta, when the contents become a faint rose colour, with a more deeply tinted outline, at least in part of their circumference: occasionally a definite part, like a nucleus, is recognisable. In the highest class of Vertebrates the several tissues of the body are best defined and, so to speak, most highly finished: the condition of organic matter by and through which the acts of addition and subtraction are performed in relation to the growth, maintenance, and renovation of such tissues is the formified proteine substance, or organite. It would seem that mere fluid would not serve the purpose: the more solid particles, 1 CLXXIX", p. 474. This idea has received confirmation in various degrees; e.g., by Quekett (Med. Gazette,' January, 1840), by Martin Barry (Philos. Trans.' 1840, p. 595), by Wharton Jones (ib. 1846); and more recently by Dr. Roberts, of Manchester, in his instructive researches, aided by the effects of a solution of magenta on the blood. The pale corpuscles were more strongly tinted than the red; and their nuclei were displayed with great clearness, dyed of a magnificent carbuncle-red. A number of the nuclei were seen in the process of division, more or less advanced, and in some cells' (my 'granulate vesicles') 'the partition had issued in the production of two, three, or four distinct secondary nuclei. There was evidence that these secondary nuclei were set free in the blood, and, by subsequent enlargement and change of form and chemical constitution, developed into red blood-discs.'-Proceedings of the Lit. and Phil. Society of Manchester, 1866. called blood-discs, added to the liquor sanguinis,' move in single file along the terminal capillaries of the circulating system and here come into the requisite contact with the tissues for the interchanges in question. One visible result of the giving and taking through attracting and repelling forces, usually defined as 'vital,'' is the change of colour which here takes place, viz., from florid to modena, in the general system, and the reverse in the respiratory one. Agreeably with this view of the function of the blood-discs we find them, in relation to the grade of histological development in the class, to be the most numerous and most minute relatively to the bulk of the body, in the present: in other words, the collective circulating surface effecting organic interchange is greatest in the blood of Mammals. The blood-discs are squeezed in the narrowest tract of the capillaries, and by their elasticity resume their shape in the wider part they are not constantly separated by plasma from the capillary wall, and the thickness of that wall is very inferior to that of the membrane which experiments have shown to allow of endosmotic transit of matters. The mammalian blood-corpuscle, as a general rule, is a circular disc; and, instead of being swollen in the centre by a nuclear part, is there thinner; the disc is consequently slightly biconcave: it consists of the albuminoid coloured matter, insoluble in serum, called hematosine, the particles of which have aggregated, according to their formifying forces, into the discoid shape. The colour of the individual blood-disc is yellow; lighter in the middle where it is thinnest, deepening to a red tint only when light is reflected from a thickness resulting from an aggregate of many discs: the quantity of the discsubstance similarly affects transmitted light. 00 The average diameter of the human blood-disc is 30th of an inch (vol. i, fig. 8, a). I early availed myself of the menagerie of the London Zoological Society to test the characters of size in the Mammalian class, and communicated the two extremes, observed, e. g., in the Elephant and Pygmy Musk (ib. b), with some other instances from different orders, including Marsupials and Monotremes, so far as to determine the class-characteristic afforded 1 Tous les faits les mieux constatés me semblent montrer que les globules du sang ne sont pas de simples concrétions inertes de matière animale résultant d'une sorte de précipitation ou de coagulation sphéroïdale; que ce sont au contraire des parties vivantes;' ccxxxix. p. 80. Nevertheless if, as Acherson thought he observed, (CLXXXII") the white or granular globules should be a result of reaction of oil-like particles on proteine-matters in plasma, their manifestation of forces, though called vital,' would not be valid against an observed mode of spontaneous generation' or 'formifaction' of such globules. 1 T28 00 1 2500 00 4800 by the size of the blood-discs. In every individual a certain range of size was presented, and the two extremes and the average were recorded thus, in the Indian Elephant, the largest blood-discs were twice the size of the human, and the smallest was not less thanth, the average being th of an inch. In the Chevrotain (Tragulus Kanchil) the average diameter of the blood-disc was 12th inch. In the Giraffe the average size of the blooddiscs was th inch, or nearly one-third smaller than those of Man; the two extremes were 4000th (few in number), 4th of an inch (more in number). The result of the examination of the blood of the largest of the ruminating tribe indicates that the size of the blood-discs relates to the condition of the whole organisation rather than to the bulk of the species. It would appear from the examination of the blood-discs in the goat, sheep, and ox, that an unusually small size of the blood-discs was associated with the peculiarities of the ruminant structure.' This generalisation has not been affected by later observations. MANDL had discovered in the Dromedary that the blood-discs were elliptic. I confirmed the fact, giving the long diameter of the average-sized discs as 3800 th inch, the short diameter th inch; but I remarked that among the elliptical discs were a few of a circular form. Extending the observation to the smaller South American species of the aberrant ruminant family, I found the elliptical form to prevail in the blood-discs of both Llama and Vicugna. In the latter the average dimensions were, in long diameter 443, short diameter 861. Mr. Wharton Jones subsequently observed blood-discs of a circular form with the more numerous elliptic ones in the Llama. These exceptional instances to the Mammalian form of blood-disc are not associated with any other approximation to the oviparous type: the oval kind are equally non-nucleate with the ordinary circular blood-discs, and adhere to the ruminant characteristic of minuteness of size. Within the limits of that natural group, it will be observed that there is a ratio between the size of the blood-disc and that of the animal. But such ratio is quite inapplicable to the Mammalian class generally. If the Camelide repeat a reptilian shape of blood-disc, the Sloths have the largest blood-discs in proportion to the body: but neither one nor the other character occurs in the Monotremes and Marsupials which combine the greatest proportion of oviparous characteristics in their Mammalian organisation. In the Echidna and Ornithorhyns Ib. p. 284. • CLXXXI". P. 73. CLXXIX". 2 Ib. 5 00 chus the blood-discs are circular and average th inch in diam. being larger in proportion than in Man, though less than in the Sloths. The numerous and insignificant gradations of size of Mammalian blood-discs between the two extremes noted in CLXXIX" have been recorded, decimally, in cCXXXIX, vol. i. p. 84. § 347. Heart of Mammalia.-In Mammals, as in other Hæmatothermals, the venous and arterial parts of the vascular system have no communication, beyond the heart, save at the peripheral capillaries. The right auricle is less definitely divided into 'sinus' and ' auricle' proper than in Birds, and the intervening valves, always less efficient against reflux from the auricle into the sinus, gradually disappear. The right auriculo-ventricular valve resembles in structure the left, as being membranous and attached by tendinous threads to muscle. Other differences between the circulating systems of the two hot-blooded classes are shown by blood-vessels. The heart, with its bag, or pericardium, is exclusively located in the thorax, and in many Mammals is more or less separated by a lobe of the lung, fig. 308, n, from the diaphragm, q. A. Heart of Lyencephala.—In the Ornithorhynchus, fig. 308, a. b, c, it presents a rounded oblong, scarcely conical, form; it is situated in the middle of the fore part of the chest, parallel with the axis of the cavity, inclosed in a thin subtransparent but strong pericardium. The right auricle, b, is larger and longer than the left; its appendix is free and is slightly bifid. It receives the venous blood by three great veins; the left precaval, ƒ, descending behind the left auricle, c, to join the termination of the postcaval, h; to the right of which the coronary vein also terminates in the auricle. The right precaval, e, is joined to the left by a transverse branch, g. There is a deep but closed fossa ovalis near the upper extremity of the septum of the auricles; indicating that the intra-uterine existence of the young was of longer duration than in the Marsupials. The right ventricle, a, is capacious, with thin parietes. The tricuspid valve consists of two membranous and two fleshy portions: the smallest of the latter is situated nearest the origin of the pulmonary artery, and corresponds with the lesser fleshy valve in the heart of certain Birds (vol. ii. p. 188, fig. 92, m): it is attached to the whole of the side of the first or adjoining membranous portion. The second fleshy portion answers to the larger muscular valve (ib. fig. 92, 1). The two edges of the lower half of the second fleshy portion of the valve in the Ornithorhynchus are free; but those of the |