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Show 296 • ME. W. E. COLLINGE ON THE [Apr. 2, VII. SUMMAEY. The more important features set forth in the foregoing pages may be summarized as follows :- (a) The sensory canal system in the Physostomous Teleostei is widely removed from that present in the Elasmobranchi, but shows many affinities to that in the Ganoidei, e. g. the manner in which the canals and branches are protected and the dermal character of the lateral canal, in many forms. (b) Tbe species of the different families differ largely from one another, and in some particulars either agree with more specialized or generalized fishes ; e. g. in Salmo the main canal of the head and the supra- and sub-orbital branches &c. are protected by a series of small drainpipe-like canal-bones not unlike those described and figured in Polyodon and Acipenser (3. p. 524), while in Conger and partly in the Siluridce the branching is not unlike that which obtains in many Anacanthinous forms. (c) The cluster-pores and primitive pores are in the majority of cases few in number, as are also the sensory organs in the canals and branches. (d) In the Siluroids the results obtained support the view that the sensory canal system in this family is one which once was much more* complicated in its nature and has since degenerated. The facts which favour such a view are :- a. The fewness and smallness of the cluster-pores. b. The exceedingly minute primitive pores. c. The dimensions of the canals and branches. d. The many indications, in various bones, of pre-existing canals. (e) Excepting in Callichthys and Esox all the branches on the head pass off from the main canal. (/) The presence of grooves in various stages of development in Pimelodus affords an instance of the manner in which the canals are formed and further how in their earlier condition they resemble that common to the adults of more generalized fishes. (g) The succession of canals in Salmo is exceedingly interesting, showing as it does a series of functionless canals passing through the substance of the bone and which once probably communicated with the surface by a series of pores. By a later anastomosis of these pores and a growth of small drainpipe-like ossifications a second and more superficial series of canals arose, which gradually replaced altogether those traversing the deeply-seated cranial elements. (h) Wherever the branching of the main canal and branches is great, and the sensory organs in the same more numerous, there is a corresponding increase in the branching of the trigeminal group of nerves. (i) The nerve-supply is fairly constant throughout the suborder, but there is some slight interchangeability, which is set forth in the following table;- |