NOTES AND MEMORANDA. 403 



as it is shown to be equal to 8 centimetres of mercury, whereas in 

 Testudo it is only from 30 to 50 mm., and only 70 mm. in Coluber natrix. 



The lacuiife so common in the vascular system of other Mollusca 

 are here replaced by capillaries, and there does not seem to be in 

 the CejjJialojwda any means by which the sea-water is enabled to mix 

 itself with the blood. 



Excretory Organs — The Octopus is provided with peritoneal caeca, 

 which contain a clear, and at times viscid, liquid, which holds in 

 suspension a number of brownish granular bodies, crystals of carbonate 

 of calcium, epithelial cells (and parasites, the most interesting of 

 which is the curious Dicycma iijims of Van Beneden). There is no 

 reason for supposing that these structures belong to an aquiferous 

 system, as their orifices are ordinarily closed, and the contained liquid 

 is a secretion from the glandular appendages of the veins, and is of 

 the natiu-e of an effete body. M. Fredericq has been unable to find 

 the uric acid which Harless and Bert had found in Sepia, but he has 

 discovered in its place the presence of guanine, and he gives, as we 

 need not do, the method by which he proceeded. 



Bespiratory System. — To deal with the nerves by which the 

 alternate opening and closing of the muscular mantle around the 

 respiratory cavity is effected : all these are given off from the sub- 

 cesophageal ganglionic mass, as may be shown experimentally by first 

 removing the whole of the head, when the respiratory movements 

 cease altogether, and then removing the supra-ceso^jhageal ganglia, 

 when they are in nowise affected. These movements appear to be 

 reflex, as the author states that the pallial nerves also supply the 

 integument of the mantle, and that section completely destroys all 

 sensibility in these parts. Excitation of the peripheral end of the 

 pallial nerve or direct irritation of the pallial ganglia produces ener- 

 getic contractions, while excitation of the central end of the nerve 

 gives rise to symptoms of distress. Section of the visceral nerves 

 ordinarily arrested the respiratory movements immediately, but exci- 

 tation of the central end, if sufficiently strong, produced a temporary 

 reaction; this excitation seems to pass to the sub-oesoi)hageal mass, 

 and thence by the pallial nerves ; the former or visceral set seem, 

 among other things, to give sensibility to the branchiae, and the con- 

 stancy of the respiratory movements seems to depend largely, if not 

 entirely, on their integrity ; these movements then are reflex, whereas 

 M. Fredericq, like most modern physiologists, regards the action in 

 the Mammalia as automatic. The question now arises, how does the 

 respiratory centre, if there is one, of the Cej^halopoda act under the 

 irritation of alterations in the characters of its air-supply ? The 

 answer is very remarkable : interruption of the cephalic circulation 

 diminishes and slows the respiratory movements, a stay in poorly 

 aerated water has the same effect, and a return to water from air is not 

 accompanied by an increase, but by a decrease in the number of the 

 respiratory movements. 



Digestive Organs. — The contents of the intestine, the secretion 

 of the salivary glands and of the liver, are distinctly acid ; the 

 aqueous infusion of the fresh salivary gland has no action on starch, 



2 D 2 



