66 ZOOLOGY. 



seventy-six seconds. When the divers emerge, the face is strongly injected, 

 and they often bleed freely from the nose, and sometimes from the ears and 

 eyes. They dive three or four times in an hour, and upon emerging, they 

 put on thick woollen cloaks. The sea is sufficiently clear to enable divers 

 to see objects at the depth to which they go. 



The Phocidse (seals) remain fifteen minutes under water, having not only 

 large lungs, but an adapting peculiarity in the circulation. In a state of 

 inaction they can remain much longer, and when on land as much as two 

 minutes sometimes elapses between each inspiration. According to 

 Frederic Cuvier, the seals in the Paris collection sometimes slept with the 

 head under water for an hour at a time, a period which exceeds that of a 

 harpooned whale. In the case of the whale, however, there is great 

 muscular action, which requires more oxygen than a state of repose 

 demands. 



§§ Dimyaria. 



The second section, Dimyaria, of the tribe Elatobranchia, includes the 

 two sub-sections, "Mytilacea and *'"Caj'diacea^ the first of which includes 

 the four families, 1. Mytilidae ; 2. Arcidae ; 3. Unionidae ; 4. Carditidae. 



Fam. 1. Mytilidm. Tliis family includes the genera Mytilus (j!>Z. 76, 

 fig. 22) and several allied genera, and Pinna {figs. 18, 19). These 

 animals have a linguiform foot, which secretes a byssus by which they are 

 attached to rocks, the byssus being at first applied by the foot. The shell 

 is equivalve, but very inequihiteral, so that the umbones or beaks, which are 

 usually situated about the middle of the back, are here placed at or near 

 the anterior extremity of the shell. In Mytilus the lobes of the mantle are 

 disunited, except at a single point posteriorly, which separates the anal 

 siphon. The anterior adductor muscle is much smaller than the posferior 

 one. Lithodomus is a sub-cylindrical bivalve, which, in its young state, is 

 suspended to rocks by a byssus ; but it subsequently perforates the rocks, 

 and lives in a cavity but little larger than tlie shell, and then the byssus 

 disappears. 



The genus Mytilus is used for food, under the name of mussel. Mytilus 

 choros, which is found at Chiloe and other parts of the western coast of 

 South America, attains a length of seven or eight inches ; and as the animal 

 is as large as the egg of a goose, and of a fine flavor, it is much esteemed. 

 The favorite mode of cooking it is to make a fire upon flat stones in a pit, 

 and when these are sufficiently heated, the fire and ashes are removed and 

 the shell-fish deposited, and covered, first with leaves, &c., and then with 

 clay. Tliis mode of cooking is practised on the coast of Australia, and in 

 jthe islands of the Pacific. 



The common mussel, Mytilus edulis, is easily taken, as it lives in shallow 

 water, and even between high and low water, upon both sides of the north 

 Atlantic. The shell is smooth, and of a blue or violet color. This species 

 is poisonous to some constitutions, perhaps one in a hundred, and it is 

 possible that this quality depends somewhat upon the season. An emetic, 

 followed by castor oil, is recommended when bad symptoms arise from 

 eating this shell-fish. The symptoms appear in one or two hours, and they 

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