ZOOLOGY. 719 



is supposed that the action of the ferment ought to be considered sep- 

 arately from that of hydration. " If in any animal raw starch becomes 

 saccharified, we must suppose that it has been previously hydrated 

 under conditions which are as yet unknown to us." 



The so-called liver of the Cephalopods has furnished no evidence as 

 yet that it forms glycogen, and, from a physiological point of view, it is 

 rather a pancreas, inasmuch as it contains a peptic aud a diastatic fer- 

 ment. The development of the last ferment in carnivorous animals it 

 is difficult to account for. {Arch. Zool. Exper. et Gen,, vol. x, pp. 385- 

 423; J. E. M. 8., (2), vol. Hi, p. 63G.) 



X. VERTEBRATES. 



Families of Vertebrates. — From a recent census taken by the present 

 writer, it appears that there are nearly 800 families of vertebrate ani- 

 mals, extant or extinct, now known. This estimate is on the basis of 

 the groups admitted as such in the "Arrangement of the families of 

 fishes" by Gill, the "Checklist of North American Batrachia aud Eep- 

 tilia, with a systematic list of the higher groups" by Cope, and the 

 "Arrangement of the families of mammals" by Gill, for the classes 

 therein considered, and various later contributions to our knowledge, 

 affecting the number of the existing but still more of the extinct groups. 



The families of the several classes of vertebrates thus recognized 

 seem to be reduced to a common standard of value almost as much as 

 can be done in the present state of our knowledge for quite unlike types, 

 and of course it must be a matter of opinion as to the degree to which 

 the ideal has been realized. Most of the families, at any rate, rest upon 

 a tolerably sound morphological basis; but among the passerine birds 

 many groups designated as families are fouuded upon the most super- 

 ficial external characters, such as the extent of atrophy or development 

 of a wing-feather (the first primary), the existence or want of a notch 

 in the sheath of the upper jaw, the degrees of extension of one or oth- 

 ers of the wing-feathers, &c. It is manifest that such characters have 

 not of themselves the significance of the modifications which differen- 

 tiate families in other classes. It is indeed possible that in some cases 

 differences of that kind may be coincident with true morphological va- 

 riations, and if such proves to be the case, the trivial features in ques- 

 tion may be employed for diagnosis and as the indices of the morpho- 

 logical characteristics with which they happen to be concomitant. It 

 is scarcely probable, however, that such will be found to have been 

 often the case, and at any rate the present use of the features referred 

 to for family distinction is an illegitimate anticipation of what may be 

 hereafter discovered. The progress of discovery may reveal that there 

 has been much sagacity and prophetic insight exhibited in the appreci- 

 ation of the true relations and grouping of families, but past discoveries, 

 and especially within the last few years, do not hold out the anticipa- 

 tion or hope that such sagacity and intuitive genius have been often 

 displayed. But whatever may be the eventual outcome, the following 



