164 NOTES AND MEMORANDA. 



quite as valid as applied to microscopic objects in general ; and he 

 therefore adopted this size (25 X 45 mm.) for his own preparations, 

 which he considers have proved very satisfactory indeed.* 



The Termination of the Visceral Arterioles in Mollusca. — 

 Thirty years ago Milne-Edwards showed that in different parts of the 

 body of molluscs there were no capillaries, like those in Vertebrata, 

 establishing a continuity between the arterial and venous systems, the 

 blood from the arteries spreading through the more or less irregular 

 spaces called lacunce by Milne-Edwards. 



In some molluscs the whole visceral cavity acts as one vast lacuna, 

 and if for instance Arioii rufus is injected by one of the tentacles, the 

 cavity is first filled and then the whole vascular system. 



M. S. Jourdain has investigated f the manner by which the 

 arterial blood passes into the visceral cavity in Arion rufus. 



If there is placed under the Microscope a fragment (cut tan- 

 gen tially) of one of the organs contained in the general cavity, and 

 the external surface is examined under a power of 200 to 250 

 diameters, it is seen that the final ramifications of the arteries 

 (the diameter of which is variable) all reach the free surface of the 

 organs, and that there they terminate abruptly by a truncated and 

 wide-mouthed extremity. It is by these orifices, nearly always 

 widely funnel-shaped, that the arterial blood passes into the general 

 cavity. 



This curious anatomical disposition seems to have been observed 

 by Alder and Hancock, though its true signification escaped them. 



M. Jourdain thinks that the orifices of the so-called aquiferous 

 vessels of the Acephala and other Molluscs are of the same nature 

 as the arterial openings above described. 



Hsemocyanin a new Substance in the Blood of the Octopus. — 

 M. L. Fredericq has discovered | in the liquid part of the blood of 

 Octopus vulgaris, a colourless albuminoid substance which he calls 

 haemocyanin (at/x-a, blood, and Kvavos, blue) as it forms with oxygen 

 a combination of a deep blue colour. A vacuum, or contact with the 

 living tissues, is sufficient to drive off the oxygen. 



This substance plays the same part in the respiration of the 

 Octopus as haemoglobin does in that of the Vertebrata. It is charged 

 with oxygen in the branchiae of the animal, and then going into the 

 arterial system and the capillaries, it gives up the oxygen to the 

 tissues. The venous blood is colourless, and the arterial blood a 

 deep blue. These changes of colour are clearly due to the fact of 

 respiration, as may be demonstrated by laying bare the great cephalic 

 artery. The blood is seen to be blue while the animal respires 

 normally in the water, but if the respiration is impeded by the animal 

 being taken out of the water or by introducing the fingers into the 

 pallial cavity, the arterial blood loses colour and takes a pale 



* Mr. S. H. Gage, in ' Amer. Quart. Mic. Journ.,' vol. i. (1879) p. 160. 

 t ' Comptes Rendus,' vol. Ixxxviii. (1879) p. 186. 



X Ibid., vol. Ixxxvii. (1878) p. 996, and ' Bull. Acad. Eoy. de Belg.,' 

 vol. xlv. (1878). 



