* Memoire sur la Poulpe. 1 Jbid.

(1556). Mayer* not only adopts the last of the above-mentioned suggestions relative to the nature of these spongy appendages to the great veins of the Cephalopoda, but ventures to bring forward an opinion that they perform the office of the kidneys of higher animals, and separate from the blood a fluid analogous to the urinary secretion; so that, according to this view, the anatomist referred to does not scruple to designate the chamber called by Professor Owen the "pericardium" as a urinary bladder; and to the two orifices leading from thence to the cavity in which the branchiae are lodged he would assign the name of urethras. Professor Owen has suggested that, in addition to their subserviency to secretion, these appendages to the veins of Cephalopods may be provisions for enabling their sanguiferous system to accommodate itself to those vicissitudes of pressure to which it must be constantly subjected, and that they bear a relation to the power possessed by these animals of descending to great depths in the ocean, - thus answering the same purpose as the capacious auricle and the large venous sinuses that terminate in the heart of fishes.

According to this view, these follicles relieve the vascular system by affording a temporary receptacle for the blood whenever it accumulates in the vessels, owing to a partial impediment to its course through the respiratory organs, serving in this manner to regulate the quantity of blood sent to the branchiae*.

* Analecten fur vergleichenden Anatomie. 4to, 1835.

(1557). In Nautilus, Professor Owen found, in addition to the spongoid appendages connected with the veins, lodged in what he denominates the "pericardium," that the great trunk of the vena cava itself presents a structure precisely analogous to what has been already described when speaking of the venous system of Aplysia among the Gasteropoda (§ 1420), namely a free communication between the interior of the vein and the cavity of the peritoneum1. The vein is of a flattened form, being included between a strong membrane on the lower or ventral aspect, and a layer of transverse muscular fibres which decussate each other on the upper or dorsal aspect. The adhesion of the coats of the vein to the muscular fibres is very strong; and these fibres form in consequence part of the parietes of the vein itself throughout its whole course. But there are several small intervals left between the muscular fasciculi and corresponding round apertures both in the vein and in the peritoneum; so that the latter membrane at these points seems to be continuous with the lining membrane of the vena cava.

The distinguished anatomist referred to counted as many as fifteen of these openings, and most of them were sufficiently large to admit the head of an eye-probe. Here, therefore, as in Aplysia, there are direct communications between the interior of the vena cava and the great serous cavity of the abdomen; and moreover, in both instances, from the peculiar muscular structure of the vein at the part where these orifices occur, their use appears to depend on, or to be in connexion with, a power of regulating their diameters 2.

(1558). The blood derived from the great venous receptacles (fig. 290, d d) is at once conveyed to the branchiae, and distributed through all the lamellae ( g g) which enter into the composition of the respiratory apparatus. Two distinct hearts, one placed on each side of the body, are interposed between the branchiae and the great trunks of the venous system, serving by their action forcibly to drive the blood through the ramifications of the branchial arteries. These lateral hearts (fig. 290, e e) are of a blackish colour, and their walls moderately thick: internally their cavities are filled with intercommunicating cells; and moreover a strong mitral valve is placed at the orifice through which they receive blood from the veins, as well as smaller valvules at the origin of the branchial arteries.; the latter enter the principal stem of the branchiae, and, running beneath the ligament (f), divide and subdivide, so as to be dispersed over all the branchial leaflets.

* Memoir on Nautilus Pompilius, p. 34.

1 Op. cit. 2 Op. cit. p. 30.

(1559). In Septa there is appended to each lateral heart a fleshy appendage (m m), which, however, is not met with in the generality of Dibranchiate Cephalopods. These bodies are attached to the hearts by narrow pedicles; and Professor Owen considers them to be rudiments of the additional pair of branchiae met with in the Pearly Nautilus.

(1560). In Nautilus Pompilius the hearts just mentioned do not exist, doubtless because the greater extent of surface afforded by the four branchiae of this Cephalopod renders the presence of extraordinary agents for impelling the blood through them, in order to ensure efficient respiration, unnecessary.

(1561). After undergoing exposure to the surrounding medium in the extensive ramifications of the branchial arteries, the purified blood is returned to the organs belonging to the systemic circulation. In Sepia it is first received from the branchiae by two dilated sinuses (ii), which might almost be regarded as systemic auricles; and from these it passes into a strong muscular cavity (k), which corresponds in function with the left ventricle of the human heart, and by its pulsations forcibly propels the blood through all the arterial ramifications of the vascular system. Two aortae, one derived from each of its extremities, arise from the systemic ventricle, the commencement of each being guarded by strong valves so disposed as to prevent all reflux towards this central heart; and thus the circuit of the blood, accomplished in this complicated system of blood-vessels, is completed. In Nautilus the lateral sinuses are wanting, and the systemic ventricle is of a square shape; but in other respects the course of the circulation is the same as is above described.