OP ANIMALS. 57 



smelling. Most commonly there are small punctiform eyes, 

 belonging to the head or tentacula; the organs of digestion are 

 very varied, and there is never more than one heart, which is 

 aortic: in those that are not symmetrical, it is on the left side 

 for the greater number, and in those that are, on the right. 

 The respiratory organs vary greatly; the greater portion of them 

 have branchia?, and some breathe air. The same variety exists 

 in their modes of generation, being unisexual without copula- 

 tion, hermaphrodite with a mutual coitus, and separate sexes. 



The pteropoda consist of a small group of mollusca between 

 the acephala and the cephala. 



51. The cephalopoda, form a small class that comprises 

 the inarticulated animals the most complex in their organiza- 

 tion, and which, like the Crustacea, among the articulata, ap- 

 proximate the most to the vertebrata. 



They are soft animals, whose bodies are wrapped in a sac 

 formed by the mantle, the sides of which project more or less 

 in fins; through its opening passes a round head, crowned with 

 feet or fleshy arms, provided with suckers which serve for 

 walking, seizing, and swimming. The mouth, situated be- 

 tween the bases of the feet, is armed with two strong jaws of 

 horn, resembling the beak of the parrot; there is a tongue that 

 bristles with horny points; an oesophagus swelled into a crop, a 

 second muscular stomach like a gizzard, and a third one that is 

 membranous; a simple and short intestine ends in the opening 

 of the sac before the neck. There is a double system of veins 

 and arteries, two branchial and one aortic ventricle. The res- 

 piratory organs are two branchiae, situated in the sac where the 

 water for breathing comes and goes. The liver is very large 

 and discharges the bile by two ducts into the third stomach. 

 These animals have a peculiar black secretion produced by a 

 gland and deposited in a reservoir. The sexes are separate; 

 there is an ovary, two oviducts, that take and convey the eggs 

 thence out of the body through two large glands that envelop 

 them with a viscid matter, and unite them in clusters; there is 

 a testicle and a vas deferens which ends in a fleshy penis by 

 the side of the anus, where terminate also a vesicula seminalis 

 and a prostate. Fecundation is performed, it is presumed, by 



