This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
(1562). In the Poulpe (Octopus vulgaris)*, the blood thus distributed through all parts of the body by the arterial vessels returns towards the branchiae through a system of venous canals composed partly of vessels furnished with distinct parietes, partly of a series of lacunae or spaces only circumscribed by the circumjacent parts.
(1563). The veins derived from the anus and the cephalic region, in conjunction with those of the siphuncle and the great visceral veins, at length unite and form by their union the two venae cavae (fig. 290, d d), through the intervention of which the greater part of the blood is conducted to the preliminary hearts (fig. 290, e e.) So far these venous trunks offer no very striking peculiarity, but arrived in the vicinity of the gizzard they present a very remarkable arrangement: instead of being formed by the junction of other smaller veins, they become uninterruptedly continuous, with an immense venous reservoir which occupies all the dorsal aspect of the abdomen, and, indeed, they seem to be a continuation of this membranous reservoir. It is to M. Delle Chiaje1 that the merit belongs of having first indicated the existence of this curious arrangement; but while the illustrious Neapolitan naturalist regards it as being simply a large venous sinus, Milne-Edwards looks upon it as being the visceral cavity itself, lined with peritoneum, as in the higher animals, into which the blood is received, and wherein it bathes directly the pharyngeal mass, the salivary glands, the stomachs, and the other principal viscera. In the Cuttle-fish (Sepia) and in the Calamary (Loligo), the above peculiarities met with in the "Poulpe" do not exist, so that there is a remarkable accordance between the internal structure of these Cephalopods and the zoological characters furnished by the number of their cephalic appendages.
In those genera furnished with only four pairs of arms the venous system is semi-lacunose in its character, whilst in the ten-armed races it is entirely vascular throughout the abdomen, although it still presents a lacunose character in the cephalic region.
* Milne-Edwards, Ann. des Sci. Nat. 1845, torn. iii. p. 346.
1 Istituzioni di Anatomia e Fisiologia Comparata, parte 1a, Animali senza Ver-tebre del Regno di Napoli, torn. i.
(1564). In the nervous system of the Cephalopoda we may naturally expect to find not only a superiority in the development of the nervous centres, as compared with the condition of these important masses in the lower Mollusca, but some indications at least of an approximation to that arrangement so eminently characteristic of the vertebrate division of the animal world, to the confines of which we are now gradually approaching; more especially as, in the activity of the movements of these creatures, and in the increased perfection of their senses, we have abundant evidence of the elevated position assigned to them when contrasted with other mollusks of less carnivorous and rapacious habits.
(1565). The nervous ganglia from whence the muscles and viscera derive their supply are still numerous and widely scattered; but their size is considerable, and proportioned to the importance of the organs over which they preside. It is to the encephalic portions of the nervous system, however, that we must principally turn our attention if we would rightly estimate this part of their economy; and these, we at once perceive, have in the class before us attained to such magnitude and importance that they emulate, no longer dubiously, the brain of a fish, with which it is not difficult to compare them.
(1566). In a Cephalopod the encephalon (for so we now may truly call it) is enclosed, as has been already noticed, in a distinct cartilaginous skull, which embraces it on all sides and defends it from injury. The capacity of the cranial cavity, however, is more than sufficient to contain the brain; and, as is the case in fishes, the interspace is filled up with a semigelatinous substance. The brain, moreover, still forms a ring, through which the oesophagus passes; so that we might with propriety preserve the terms supracesophageal and infraoesophageal ganglia, were these parts not now become so intimately united to each other that they seem fused into a single mass (fig. 294, a, 6), from different portions of which, nerves serving very different offices take their origin.
(1567). In Nautilus the nervous system has been most minutely and critically examined; and the important deductions to which the researches of Professor Owen point, relative to the analogies that may be traced between the encephalon of these creatures and the brain of higher animals, have served to attach an interest to the study of this part of the economy of the Cephalopoda which has scarcely as yet been sufficiently appreciated by physiologists.
(1568). In the Nautilus Pompilius, the supra-oesophageal ganglion of the Gasteropoda is represented by a thick round cord of nervous matter (fig. 291, l), which is in communication with two nervous collars (3 3, 4 4) that surround the oesophagus, and likewise with two large ganglia (2) from which the optic nerves take their origin; but in the Cuttlefish the same portion of the nervous system (fig. 294, a) is much more largely developed, and presents a ganglionic mass of considerable size. If we inquire the reason of this want of correspondence in magnitude presented by the same organ in these two cases, we must necessarily examine the relations in which this part of the brain stands with other circumstances in the economy of the two animals in question; and we perceive, as Professor Owen has most satisfactorily demonstrated*, that the brain is here developed in accordance with the relative complexity of the organ of vision, and also with the perfection of the locomotive faculties possessed by the Cephalopods under consideration. With the exception of sundry small twigs given off to the mouth and pharynx, the optic nerves (fig. 291, 2; fig. 294, e) are the only ones derived from this part of the encephalon; and, as we shall afterwards see, both the simply-constructed eye of the Nautilus and the complicated visual organs of the Sepia are correspondent to the development of the supra-cesophageal brain; so that consequently the latter may, with every show of reason, be looked upon as the representative of the optic lobes found in the encephalon of fishes 1, and the analogue of the bigeminal bodies in the brains of the higher Vertebrata.