Venous system of the Lobster: a, side view of the venous sinus covering the stomach.

Fig. 203. Venous system of the Lobster: a, side view of the venous sinus covering the stomach; b, side view of the sinus surrounding the heart (the letter is placed near one of the valvular orifices by which the venous blood is admitted into the ventricle); c c c c, superficial dorsal sinuses.

(1020). Several large arteries are derived from the above-mentioned simple heart. A considerable trunk (fig. 201, g) goes from its anterior extremity to supply the eyes, antennae, stomach, and neighbouring organs; another, the hepatic (i), which is sometimes double, supplies the two lobes of the liver; a third large vessel (h) supplies the abdominal or caudal region; and a fourth, the sternal, derived from the posterior apex of the heart, bends down to the ventral aspect of the body, where it divides - the posterior division (I I) supplying the lower parts of the abdomen, while the anterior and larger division (m) gives off branches to the legs and foot-jaws (n n n n); it likewise furnishes other vessels (o o o o), which are distributed through the branchiae.

(1021). The venous system is made up of large and delicate sinuses that communicate freely with each other, and receive the blood from all parts of the body. Those of the dorsal region are represented in the opposite page (fig. 203): a large venous sinus (a) occupies the cephalic region and covers the stomach; another cavity (6) lies immediately above the heart; and a series of smaller chambers (c c c c) are situated above the muscles of the caudal region. These cavities, notwithstanding their apparent extent, are very shallow, so that, upon a transverse section, their dimensions are by no means so great as a superficial view would indicate. The sinus (6), or that placed immediately over the heart, communicates with that viscus by short trunks, the terminations of which in the heart are guarded by valves (fig. 201, fff), so disposed as to allow the blood to pass from the sinus into the heart, but prevent its return in an opposite direction.

Such is the apparatus provided in the Lobster for the circulation of the blood. Our next inquiry must be concerning the course that it pursues during its circuit through the body.

(1022). MM. Audouin and Milne-Edwards*, after very minutely examining this subject, came to the conclusion that the heart is purely of a systemic character, being only instrumental in propelling the blood through the body, but having nothing to do with the branchial circulation; they conceived that the circulating fluid, having been collected in the venous sinuses, was brought to the roots of the branchiae, over which it was distributed by venous tubes, and then returned to the heart by vessels, which they call branchio-cardiac, to recommence the same course. The appended figures, however, which are accurately copied from engravings of the Hunterian drawings in the collection of the Royal College of Surgeons of England 1, would seem to give great reason to doubt the accuracy of the conclusions arrived at by the eminent naturalists referred to, and to show that the heart, instead of being purely systemic, is partly branchial, and impels the blood, not through the body only, but also to the respiratory organs. This view of the subject, which we are disposed to consider as the most correct, is exhibited in the diagram annexed.

Setting out from the heart, we find that the blood goes to all parts of the body through the different arterial trunks, and by the great sternal artery (fig. 201, k) is conveyed to the legs, foot-jaws, and false feet. But from this same artery (m), vessels (o o o o) are furnished to the branchiae. The branchial arteries so derived (fig. 204, g) subdivide into secondary trunks (h h h), which ramify through the individual branchiae and supply all their appended filaments. Having undergone exposure to the respired medium, the blood is again collected from the branchiae by branchial veins (k k k), represented on the opposite side of the body, and conveyed by the large vessel (I) to the dorsal sinus (fig. 203, 6), where, being mixed up with the general mass of blood contained in the sinus, the circulating fluid is admitted into the heart through the valvular orifices (fig. 204, d d), to recommence the same track.

* "Recherches Anatomiques et Physiologiques sur la Circulation dans les Crustacea," Ann. des Sci. Nat. torn. ii.

1 Catalogue of the Physiological Series of Comparative Anatomy contained in the Museum of the Royal College of Surgeons of England, vol. ii.

Transverse section of the body of a Lobster, just behind the heart.

Fig. 204. Transverse section of the body of a Lobster, just behind the heart: a, cut edge of the shell of the back; b, the under surface or sternal aspect; c, the posterior end of the heart; d d, two orifices of veins entering the heart; e, cut end of the superior caudal artery; f, the trunk of the large artery (sternal) going to the legs and gills (k in fig. 201); g, trunk of an artery going to supply one tier of gills; h h h, the branches going to each gill; i, artery of the leg; kkkk, the internal vessels or veins from each gill; I, the common trunk or branchial vein; m m, the gills; n n, the flabella, or laminae subservient to the movement and renewal of the respired medium; o o, basal joints of the legs.

(1023). In the Crustacea, as in the class of Insects, the blood* occupies all the interspaces left between the various viscera, as well as the still smaller lacunae situated among the muscular fibres or underneath the skin: but the heart, instead of opening immediately into this system of intercommunicating cavities, as among the true insects, is continuous with a special system of tubes, the walls whereof are well defined, and of which the peripheral branches ramify in the substance of all the organs of the body, thus constituting a very complete arterial system, although, by their ultimate ramifications, the centrifugal vessels thus formed become continuous with and lost amongst the interstitial lacunae of the body, which in their turn communicate with more considerable cavities situated between the viscera; so that the blood ejected by the heart and arteries, arriving in the last ramifications of those tubes, escapes into the general interstitial lacunary system, by the intermedium of which it returns towards the heart.