536 Reviews. [July, 
important question,”’ for that the essence of all physiology points to 
the nervous system as the basis of all correct arrangements, and upon 
the presence, absence, or supposed characters of that system, he (the 
author) therefore based his classification. But supported as he was 
in this view by many men of the highest eminence, he soon found 
himself in the same dilemma in which he had placed Cuvier, the 
greatest systematic zoologist of the age ; and in a work published some 
years afterwards,* he himself acknowledged the imperfection of his 
“neural” system of classification, and stated that “in the lower forms 
of the animal kingdom especially, we are far from being able to avail 
ourselves of such a guide.” He did not venture, however, to substitute 
a better system, but employed the old one as a pis aller. 
In referring to this fact, we by no means seek to disparage the 
author’s labours in the cause of science ; on the contrary, we consider 
that the acknowledgment of the imperfection of his system redounds 
to his praise, and exhibits a moral courage not often possessed by 
scientific men. 
Turning now to the Continent, we find two recent works on system- 
atic zoology, both still regarded with great favour in scientific circles, 
and the authors of which have built their systems upon almost entirely 
dissimilar foundations. In his Guide to the Study of the Invertebrata,t 
Siebold has founded his classification upon the form and structure of 
animals, ranging them according to the simplicity or complexity of their 
organization, and availing himself of all known data of structure and 
development; whilst Vogt (whose work, with all its imperfections, is 
perhaps the best zoological handbook extant) t has built up his system 
solely upon the phenomena of development. 
Nor is it surprising that Vogt should have singled out these 
phenomena; and although we shall presently perceive that his system 
was as much open to objection as that of other naturalists who direct 
their chief attention to one phase only in animal existence, we cannot 
be surprised at his having selected this one, for at the time he under- 
took his task, every day was revealing new features in the develop- 
ment of animals which appeared to set at defiance all previous modes 
of classification. To speak popularly, Echinoderms were found, first, 
to lead the life of “ Acalephs ;” Medusz, that of the hydra; winged 
insects gave birth to others without organs of flight, and these again 
produced offspring resembling their grandparents; creatures that 
swam freely about in the water appeared to become degraded, and to 
belong to quite a different class, as entozoa, when their old habitat 
was changed for the internal organ of some warm-blooded creatures : 
and thus it became as difficult to define the true position of a vast 
number of animals which, in various stages of their existence, changed 
their form and character, as it would be for an uneducated man to 
* «The General Structure of the Animal Kingdom.’ Van Voorst. 
+ ‘Lehrbuch der Vergleichenden Anatomie der wirbellosen Thiere,’ by C, 
Th. V. Siebold, being the first volume of the ‘ Lehrbuch der Vergleichenden Ana- 
tomie,’ by Siebold & Stannius. Berlin: Veit & Co., 1848. 
+ Zoologische Briefe: Naturgeschichte der lebenden und untergangenen 
Thiere.” 2 vols. Frankfort am Main Literarische Anstalt. J. Ruetten, 1851. 
