INFLUENCE OF LATERAL-LINE CANALS 331 
The form of the spicule may depend on its chemical nature, its 
mineralogical condition and on the influence of the surrounding 
parts. Bone in the catfish head is laid down in a non-crystalline 
form because of the slow growth; the early deposition being in 
the nature of granules, to which other granules are added. 
The spicule is directed in its early growth only by the capil- 
lary, surface, and chemical influences which prevent it from 
ranging far from the colloidal bed immediately adjacent to the 
canals. Later it must respond to the molding influence of the 
form of the catfish head and to hereditary influences. It is 
interesting to speculate that the ancient catfish had in its head 
a series of segmental bones made up of thread-like spicules, 
like those seen in the young Amiurus 24 mm. long, but unfor- 
tunately the paleontology of the Siluroids is not sufficiently well 
known to prove this, the group being unknown prior to the close 
of the Mesozoic, and the Eocene species differing but little from 
the modern forms. The part heredity may play is thus im- 
possible of solution. The segmental condition is transitory, 
having disappeared entirely from the sphenotics in a 50-mm. 
larva, measured from the tip of the caudal fin. 
Another and very important influence exerted by the lateral- 
line system is that it introduces into the living, active materials 
of the young head an inactive substance, such as the canals are. 
The dense connective tissue forming the canal is protective in 
nature and inactive in function. Actual precipitation of cal- 
cium salts takes place usually, not in living, but in either dead 
or inactive material. This has been the idea advanced by 
Sims Woodhead (’89), who says that ‘‘lime salts, of whatever 
form, are deposited only in vitally inactive tissue.”’ Another 
important factor is the degree of lime salts present in the medium 
in which the animal lives and of the amount of salts taken with 
the food, since it has been seen that in the presence of excess 
of lime, the shells of various Foraminifera become greatly altered, 
strengthened with various excrescences and assuming characters 
described as proper to other species. 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 34, NO. 3 
