No. 397.] REVIEWS OF RECENT LITERATURE. 59 
the first being morphological, and the second systematic. In the first 
part the work is based entirely on embryology, and an introduction 
which sketches the main features of development is succeeded by 
the morphology of the organs arrayed in accordance with the germ 
layers. Although logically there is much to be said in favor of 
such an arrangement, it would seem hardly an improvement on the 
usual method, which begins with the skeleton and muscles, and thus 
presents a framework that may serve as a series of relations by 
‘means of which the other systems may be more easily described. 
Although permissible for an elementary text-book of general mor- 
phology where there is little or no descriptive anatomy, it would not 
seem possible to employ such an arrangement in a work upon the 
anatomy of a single animal, for historically the nomenclature of the 
bones was the first established, and organs and parts of organs have 
been named with reference to these, or to other parts which, in the 
usual order, precede them. <A second difficulty is that it is impossi- 
ble to remain consistent to such a plan, or if strict consistency be 
carried out, it is then necessary to separate most widely organs 
which should be treated together. . Thus, in the treatment of gills 
(p. 22), it becomes logically advisable to speak of the external 
“ gills " of amphibians which are strictly ectodermic and which, with 
due regard to the arrangement of the book, should come in with the 
integument (about p. 9o). Again, scales are treated under the divi- 
sion “ectodermal structures," but these include the scales of tele- 
osts which, in their completed state, are entirely mesenchymatous, 
and also the scales of Selachians which possess a double origin. 
The subject of teeth, though strictly homologous with the latter 
organs, appears with the “endodermal organs,” although their origin 
is made clear in the text, while dermal or membrane bones are 
treated under * skeleton." It is of course impossible by any arrange- 
ment always to bring correlated parts into close juxtaposition, but an 
arrangement which separates so widely three such closely related 
Structures as placoid scales, teeth, and dermal bones is certainly 
unfortunate. 
In the arrangement and nomenclature of the embryonic layers, the 
author has employed the very convenient terms * mesothelium " and 
" mesenchyme " for the two structures which arise between ectoderm 
and endoderm, and thus leaves the word “ mesoderm" to be em- 
ployed as a comprehensive term for both structures. It remains to 
be seen, however, whether the replacement of the terms “ invagina- 
tion" and « evagination " by the Saxon “ inpushing " and “ outpush- 
