1864. | Comparative Anatomy and Classification. 537 
decide whether a butterfly ought to be ranked as a worm or as an 
insect ; and it was found necessary to raise this and degrade that form 
of life, according to the stage in which it had been observed when its 
place in the animal kingdom was first assigned to it. But Vogt was 
not content to rectify the boundaries of former systems, and fill u 
gaps that had been left open through the imperfect knowledge of those 
who preceded him, The phenomena of development had taken such 
complete possession of his mind, that he allowed them to serve as his 
chief guide in classification ; and thus we have the whole animal 
kingdom divided, according to his method, into three great groups, 
each possessing, as he believed, some marked embryonic peculiarity, 
or, more correctly speaking, each having a distinct method of repro- 
duction. The lowest of these groups, comprising the forms now 
known as Protozoa, had (according to Vogt) no true ova; the second, 
embracing the Radiata, Vermes, and all the Mollusca, except the Cepha- 
lopoda (cuttle-fishes, &c.), was the result of the transformation (or 
absorption) of the whole yolk into the embryo; and the highest 
group in which he found the embryo developed distinct from the yolk 
(Gegensatz zwischen Embryo und Dotter) comprised the Cephalopoda, 
Articulata, and Vertebrata. In like manner, he was guided in the sub- 
division of these groups, especially of the last-named, by certain 
features in the development of the embryo in ovo, or of the foetus. 
This system of classification was always considered faulty by the 
leading zoologists of Germany; and we need only state that the 
Infusoria, which he classed in his group possessing no ova (kein Ei), 
have, through the recent researches of Dr. Balbiani, of Paris, been 
shown to be sexual and to produce ova; and that he would be com- 
pelled to seek some other feature in their structure or development in 
order to define their true position, to show that his system is quite as 
imperfect as those based upon any other single phase in animal life. 
But our limited space prevents us from referring to other systems 
of classification, and with a passing tribute to the great zoologist 
Milne-Edwards, the worthy disciple of the illustrious Cuvier, whose 
labours have been transferred, with or without acknowledgment, 
to innumerable so-called Hand-books and 'Text-books, which have 
been published in almost every European language, we must now 
direct the attention of our readers to the work before us. 
The first portion of the treatise, which is a reprint of a series of 
Lectures delivered by the Author at the Royal College of Surgeons, 
is devoted solely to the subject of Classification, and to the relations 
of one group of animals with another. Asa series of essays on this 
branch of zoological science, it is not only very valuable to students 
who already possess some knowledge of the subject, but will be found 
deeply interesting to more advanced readers, who have not had the 
opportunities afforded to the author of watching the progress of sys- 
tematic zoology during the last few years, or to those whose studies 
have been directed rather to practical and experimental zoology than 
to the literature of the science. 
As regards the author’s system of classification, he tells us that 
it is based “ upon purely structural considerations,” and that animals 
