432 
BULLETIN OF THE BUREAU OF FISHERIES. 
the part of the intestine which has the typhlosole feebly developed. This crystalline 
body is largest near the stomach and tapers gradually to a point and ends just beyond 
the first bend of the intestine, where the typhlosole becomes prominent. The latter 
structure is much swollen and gelatinous at this point, so that it almost obliterates the 
cavity of the intestine. 
Several theories have been advanced to explain the nature of the crystalline style. 
Mytra (io) seems to have shown pretty conclusively that it contains an enzyme which 
will digest starch. He thinks it is a secretion from the liver. Pelseneer (i i) has held for 
a long time that its function is that of protection. He thinks it forms a protective 
coat for the intestine and surrounds rough particles of sand and diatom shells which 
might otherwise injure the delicate tissues. I find a structureless coat or cuticle of 
Fig. 9. — Drawing of the digestive system in position, g, Mantle gland; m, visceral mass; o, mouth; 
s, stomach; d, ope nin g of liver ducts into stomach; i, intestine; r, rectum. 
some kind lining a considerable part of the wall of the intestine. This may be formed 
from the crystalline style and may serve to protect the epithelial lining of the intestine. 
NERVOUS SYSTEM. 
The central nervous system consists of three pairs of ganglia which are connected 
by nerve tracts, or commissures, in the usual way. One member of each pair of ganglia 
is situated on the right side of the body and the other directly opposite it on the left. 
Bach ganglion supplies nei ves to tissues situated on its own side of the body only, and 
since those of the right and left are alike in number and distribution they will be described 
as coming off in pairs. The pedal ganglia are fused more or less to' form a single mass, 
but the line of separation is plainly discernible. (Big- 10, pg.) They are situated 
at the base of the foot and they give off three pairs of nerves posteriorly which are dis- 
tributed to the byssal apparatus and retractor muscles of the foot. They also give rise 
to one pair of nerves from their lower anterior surfaces, which penetrate the foot. 
