based on the principle of Cephalization. 349 
especially to the Ganoid type, would rank low, as is obvious 
rom their exsert and loosely-hung gills without gill-covers, the 
absence of scales, and the general inferiority in all structu 
arrangements. The Ganocephs, known only as fossils and gen- 
erally regarded as Perennibranch Amphibians, have, it is true, 
a higher grade of organization, both as regards gills and scales, 
being allied, in these respects, to the highest of Ganoids. And 
this fact, in view of the above canon, sustains the opinion of 
Agassiz that. the Ganocephs (or Archegosaurs) are actually 
anoids,—having a Reptilian feature in the partial elongation 
of the limbs, but in little that is fundamental in the structure 
beyond what belongs essentially to the Ganoid-type. 
VIL. The lines of gradation between classes, orders and 
tribes, are only approximating, not connecting, lines, there being 
often wide blanks of the most fundamental character. The 
Ornithorhynchus, although Duck-like in some points, leaves still 
avery wide unfilled gap between the Mammal and Bird, and 
the Marsupials a still wider. The species are fundamentally 
ammalian, and Bird-like only in points of secondary import- 
ance. In asimilar manner, there are long blanks between the 
Ostocoids and higher Mammals; between Myriapods and either 
Insects or Spiders; between Reptiles and Mammals. e inter- 
mediate groups belong decidedly to one or the other of the two 
approximating groups, and are never strictly intermediate. 
_ VIII. Under any class, order or tribe, the lines of gradation run 
im most cases between the degradational subdivision and severally 
the gammatypic and betatypic subdivisions, and far less clearly, 
or not at all, between the gammatypic and betatypic themselves; 
that is, between D and 7, and D and @, rather than 8 andy. For 
example, in the class of Mammals, the lines run between Odto- 
coids and either Megasthenes or Microsthenes, and not distinctly 
stween Megasthenes and Microsthenes; in Insecteans, between 
Myriapods and either Insects or Spiders, and not distinctly be- 
tween Insects and Spiders; in Crustaceans, Between Entomos- 
tracans and either Decapods or Tetradecapods, and not distinctly 
between Decapods and Tetradecapods; etc. There are excep- 
tions to the canon; and still it is a general truth. _ ; 
IX. Under any class or order the line of gradation between 
the degradational and the betatypic subdivision (or D and 8) is 
often more distinct than that dts the degradational and 
gammatypic, (or D and 7), although the gammatypic is nearer in 
grade mH de Tadeo steht the lme between Myriapods 
and Insects is more distinct than that between Myriapods and 
Spiders; or that between Entomostracans and Decapods, than 
than that betweeen Entomostracans and Tetradecapods. 
There is an exception in the class of Mammals: the Odtocoids 
Seem to graduate towards both Microsthenes and Megasthenes 
“With nearly equal distinctness 
