502 WALTER EDWARD COLLINGE. 
cephali, with a view to ascertaining, like de Sede, their value 
in classification. For this system of canals, &c., Garman pro- 
posed the term Tremognosters, but it has not met with general 
acceptance, the term sensory canal being much more appro- 
priate. 
Allis (1) in 1889 dealt in an able manner with the topo- 
graphy and development of the system in Amia calva. 
Pollard (62) in 1892, following Garman, compared the canals 
in a number of Siluroids and discussed their value for purposes 
of classification. 
In 1892 Ewart (25 and 26), following up his researches 
upon the cranial nerves of Elasmobranchs, published a valu- 
able account of the system in Lemargus and Raia batis, 
the first that has attempted with any completeness to deal with 
the general anatomy of the system in the Elasmobranchii. He 
emphasised the necessity for studying this system of sensory 
canals and their innervation together. He has shown that the 
canals in the Elasmobranchii, instead of being innervated by 
the branches of the trigeminal and facial nerves—as was 
generally supposed—are supplied by the latter only and the 
vagus. He further pointed out that certain branches of par- 
ticular cranial nerves are developed solely for the innervation 
of, and in connection with, the sensory canals, and disappear 
almost, if not entirely, in the higher Vertebrates. 
In 1893 the writer published short accounts of the system 
in Polypterus, Calamoichthys (18), and Lepidosteus 
(19), and in certain fossil fishes (20). 
For many of the earlier historical details I am indebted to 
Mr. 8. Garman, C.M.Z.S., of the Museum of Comparative 
Zoology, Cambridge, U.S.A., to whose memoir the reader is 
referred for more detailed accounts of the opinions of the 
various writers. 7 
iii, NOMENCLATURE. 
It will be as well at the outset of these investigations to 
revise the nomenclature of the subject, and so avoid an endless 
confusion and series of explanations which otherwise must 
