. California pesce e selvaggina . d San Francisco Bay. *stampato su autorizzazione dell'Ufficio della pesca degli Stati Uniti. 114 caLifoknia FISRI e gioco. In struttura tlie due specie sono molto simili. Esternamente, è presente il guscio bivalve, stretto all'unvbo o al becco all'estremità anteriore,e incernierato sul retro o sul dorso 1)y un pezzo elastico di sostanza cartilaginea che tende a tirare il guscio aperto (vedi fig. 60). Internamente, il guscio è rivestito da una membrana, chiamata mantello, per la protezione dell'animale all'interno; il mantello i)spiga le ghiandole che formano il guscio che servono ad aggiungere entrambe le dimensioni
2033 x 1230 px | 34,4 x 20,8 cm | 13,6 x 8,2 inches | 150dpi
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Questa immagine potrebbe avere delle imperfezioni perché è storica o di reportage.
. California fish and game . d San Francisco Bay. *Printed by permission of the United States Bureau of Fisheries. 114 caLifoknia Fisri and game. In structure tlie two species are very similar. Externally, there isthe bivalve-shell, narrowed to the unvbo or beak at the anterior end, and hinged at the back or dorsum l)y an elastic piece of cartilage-like substance that tends to pull the shell open (see fig. 60). Internally, the shell is lined with a membrane, called the mantle, for the protectionof the animal within; the mantle l)ears the shell-forming glands thatserve both to add to the size of the shell and to repair breaks (see fig. 61).During most of the year the mantle is a very thin-looking tissue indeed, but in the spawning-season it becomes greatly thickened and swollen bythe eggs or the milt. On each side, between the mantle and the bodyof the animal are the gills, two layers of extremely delicate tissue; theycan be distinguished from the mantle by reason of the very fine longi-tudinal lines which mark them.. Fig. 60. Exterior of California mussel. Photograph by W. C. Mathews. The body contains the digestive tract and bears the foot. Inan opened mussel, one can see, at the anterior end, four leaf-like piecesof tissue growing out from around a slit-like opening; this opening isthe mouth or labium, and the pieces of tissue surrounding it are thelabial palps, which by their motion help to direct the food into themouth. The remainder of the digestive tract is rather difficult to trace;its course will be merely outlined. From the mouth the food passes intothe gullet, forward of the foot, and then into the stomach, which lies ina mass of dark-colored tissue, the so-called liver; the intestine passesback to the big posterior adductor muscle, around which it bends, thenpasses forward to the heart and back again to the muscle alreadyreferred to. Like other molluscs, the mussel has a closed circulatorysystem, with heart and blood vessels; it has also a very simple andpri
