624 



LECTURE XXIV. 



oblong pyriform shape, as in Octopus {fig. 227, d\ Sepia, and Loligo 

 {fig. 226, /) ; but it presents at certain seasons a trilobate form in 

 the Sepiola, in which Peters * has observed it to contract regularly. 

 It is a very active organ, and its inky secretion can be reproduced 

 with great activity. The tint of the secretion varies in different 

 species, as is exemplified, in its inspissated state, by the Italian pig- 

 ment called *' sepia," and the Chinese one, called " indian ink." It is 

 also very durable, as is shown by its frequent preservation in a fossil 

 state in both the extinct Calamaries and the Belemnites. It is affirmed 

 by some chemists to contain a peculiar animal principle, which Vizio 

 has termed " melanine." 



Many of the Cephalopods possess the power of emitting a luminous 

 secretion, f All of them are nocturnal and social animals, and are 

 readily attracted by bright metallic substances. 



Prior to the dissection of the Pearly Nautilus, the Cephalopods 

 were regarded as having three distinct hearts ; but two of these, which 

 are appropriated to the branchial circulation, are peculiar to the higher 

 order, and are perhaps 

 the main-spring of their 

 superior muscular ener- 

 gies. 



In the Dibranchiates 

 the venous blood returns 

 from each arm along its 

 lateral and posterior parts 

 by two veins, which 

 severally unite at the 

 base of the arm with the 

 opposite vein of the ad- 

 joining arm, the whole 

 being ultimately con- 

 veyed to an irregular 

 circular sinus, which sur- 

 rounds the pharynx, and Sepia officinalis. 

 is continued between the head and the funnel into the great 

 anterior cava {fig. 228, a). In Octopus this vessel is provided with 

 two semilunar valves at its commencement ; in Sepia with a single 

 valve. At its entrance into the pericardium it usually receives two 

 large visceral veins, returning the blood from some lai'ge irregular 



* XXIV. p. 329. 



■f- liinnsDus quotes a passage from Bartholinus, ilhistrative of the luminous 

 surface of a species of Octopus which shone so brightly, "ut totum palatium 

 ardere videretur." This phosphorescence might be post-mortem, and the result of 

 commencing decomposition. 



