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Rh wall of the former : but here, as in the other group, there is no pericardial sac.

The heart itself is strong and muscular, and the fibres are of the striated kind. Those of the branchial hearts are also apparently striated, but the striæ are less distinct, owing perhaps to the state of preservation of the specimen examined. Striated fibre has likewise been observed in these parts by H. Midler.

The ascending aorta, on reaching the cranium, is divided into two nearly equal portions, each of which has, near its origin, a conspicuous bulbous enlargement. Numerous branches radiate from these bulbs, and are distributed to the brain, to the eyes, to the œsophagus, to the salivary glands, to the buccal organ, and to the arms. The branches that go to the buccal organ pass through the nervous collar; and that which supplies the arms goes so far along with them, and then penetrating through the pedal ganglion, passes to its outer surface, and so advances to its destination, giving off, as it goes, branches to the muscular wall of the buccal channel.

The arterial branches supplying the fins in the Loliginidæ, exhibit enlargements similar to those of the aortic branches, and the function in both cases is probably the same, though it is not very clear what it is. As they are muscular, however, they are probably for the purpose of regulating the flow of the blood to the respective parts, retarding it or pressing it onward, as occasion may require.

The most interesting point that I have observed in the nervous system is, that the surface of the brain of Octopus vulgaris displays distinct inequalities, having a considerable resemblance to the rudimentary cerebral convolutions of some of the lower Vertebrata. I have also, for the second time, observed that the brachial nerves originate in two centres, or rather, that in those species which have the pedal ganglions divided into two portions, these nerves have double roots which can readily be separated for a considerable distance from their origin.

It may also be stated, that, on a due analysis of the parts, the commissures and the ganglions, composing the Cephalopodous brain, can be clearly determined, and their homological relations with those of the lower mollusks ascertained. This being so, the difficulties with regard to the general homologies of these highly organised mollusks do in a great measure disappear. And it is satisfactory to know, that the results, thus obtained, agree with those derived from embryological and other data, as determined by Prof. Huxley.

In concluding these few somewhat hasty and imperfect remarks, on the structure and physiology of the Dibranchiate Cephalopoda, it will be well to take a glance at the results at which we have arrived, though in some respects they cannot be considered final.

The results, then, are as follows:—

First.—That the so-called abdominal or visceral chamber, in the Dibranchiate Cephalopoda, is a veritable venous sinus, formed by the expansion of venous trunks, and that it is provided with proper walls.