116 = CALIFORNIA FISH AND GAME. 
probably of a glue-like consistency at first, but harden into the firm, 
stiff fibers which hold the mussel so securely to his perch. 
From now on, the mussels are practically settled for life; doubtless 
they can shift about in a very limited area on the object to which they 
are fastened, but their days of ‘‘roving’’ are ended. 
Owing to the precariousness of their existence, of the countless 
numbers of young that are produced each season comparatively few 
live to maturity and to ‘“‘ripe old age.’’ At the beginning, many 
probably fall prey to small fishes and to other carnivorous creatures ; 
many doubtless succumb to the lack of food, while still others may fail 
to find suitable places for attachment. Those that succeed in becoming 
fixed are still exposed to attacks from carnivorous inhabitants of the 
sea. Their worst enemy on the Pacific coast is the starfish, which has 
been known to destroy immense mussel beds in a short time. 
x Foster.or Retractor Muscle 
Sneii-Forming Gianas \ 
Lage of Mantie 
Abdgomen SY 
POSTERIOR END 
Byssus or “Beard 
Posterior Adductor Muscle. 
Fig. 62. Diagram showing the interior structure of a California mussel. 
Members of the species californianus mature in about two seasons, 
and in that time attain a length of from two to four inches. At the 
Scripps Biclogical Station, near La Jolla, a conerete pier was put down 
in November, 1°15; in July, 1917, two seasons later, most of the piles 
were thickly clustered with mussels, some of which were four inches long. 
It is not known what the life of the mussel is, but it probably is six or 
seven years at least, and possibly longer. 
As is the case with other mollusks closely related to it, for instanee, 
the clam and the oyster, the mussel swallows everything that comes his 
way. He simply opens his mouth, lets the sea water enter, and then pro- 
ceeds to digest and to assimilate whatever there may be of value as food. 
The water teems with organisms that are microscopic in size; among 
them are the diatoms, which are one-celled plants, and many species of 
protozoans or one-celled animals. These constitute the bulk of the food 
of mollusks hke the mussel. It has been demonstrated that diatoms con- 
stitute 98 per cent of the bulk of the food of the oyster, and the mussel 
likely uses about the same quantity of diatoms in its diet. To be sure, 
