Embryology. 1135 
as some of these are, we are still deplorably deficient in monogra- 
phies which serve to illustrate the later or post-embryonic changes, 
intervening between the last stages with which the embryologist 
cares to concern himself, and the point where the organism becomes 
adult, when it is supposed that the scalpel of the anatomist is all- 
sufficient in prosecuting farther inquiry. This is unfortunate, since 
the details of the final metamorphosis of whole systems of organs, 
even in animals as thoroughly studied as the chick, is in some 
cases scarcely at all known, or so imperfectly as to be nearly the 
same as if altogether unknown. The external features of the 
development of the skeleton of the chick are pretty well known, 
but the internal and histological changes, and the development of 
pneumaticity of the bones, quite imperfectly. ; 
Now that serial sections may be so easily prepared and photo- 
graphed upon an enlarged scale, it is strange that no one has yet 
undertaken to prepare sets of uniformly enlarged photographs of 
series of sections, arranged in a folio in the order in which they 
were cut, of the most important stages of the development of the 
chick, and thus supply a more satisfactory iconography of the 
embryology of this animal than we yet possess. Series of enlarged 
photographs of serial sections, arranged as suggested, if made with 
care, would serve almost as well for purposes of reconstruction as 
the modelling method of Born, or the method of graphic isolation 
proposed by Kastschenko. It would, in fact, make it possible to 
inspect series of sections of an organism with as much readiness and 
as minutely as one is enabled to inspect the successive pages of a _ 
book. In fact, the topography or relations of the organs, as well 
as some notion of their histological composition, in an embryo, in 
Successive planes, could be as readily got at in this way as the text 
‘imprinted upon the pages of a book. If thin gelatine positives of 
such series were properly prepared, protected, and arranged in their 
proper serial order, in the form of a roll, series of sections could be 
projected, one section after the other in succession, upon a screen for 
purposes of lecture demonstration, in a manner far more effective 
than would be possible with the most complete serial sets of dia- 
grams.—J, A. R. 
