Nova Acta Academie Nature Curiosorum. 369 
followed up from their first appearance to their complete evolution; and 
the various gradations of form which they successively assume, at different 
periods and in different animals, are traced with great minuteness, Of 
the facts thus ascertained the most important, as well as the most un- 
expected, is the existence in the higher Classes of Vertebrata, at a very 
early period after the impregnation of the ovum, of organs corresponding 
to the the temporary branchie of the Batrachian Reptiles, and the 
permanent gills of Fishes. The discovery of these organs in the egg of 
the common fowl was first announced by Dr. Rathke in the “ Isis’’ for 
1825; and afterwards extended by him to the embryos of Swine, Horses 
and several ruminating Quadrupeds, and finally to that of the human 
species. Several other comparative anatomists have since turned their 
attention to the same object; and their labours have produced not only 
a positive corroboration of the observations of the original discoverer, 
but also much additional information. The most successful of these 
investigators are M. Huschke, whose papers also appeared in the “ Isis’’; 
and Dr. von Baer, whose memoirs are contained in Meckel’s Archives of 
Physiology, and in the “‘ Annales des Sciences Naturelles.”” So much 
in fact has been written on this highly important discovery both previously 
and subsequently to the publication of the paper now before us, that it 
would be impossible to do justice to the subject by a simple abstract of 
its contents; while to enter into a general analysis of all the papers to 
which we have referred would occupy too much of our space. We must 
therefore rest content with having indicated where ample information may 
be found by those who are desirous of entering fully into this curious 
investigation. For the benefit of those who may not have it in their 
power to make these references, but who may be desirous of verifying 
for themselves the leading facts on which the theory is based, it may not 
be superfluous to add, that the period when the branchial apertures on 
the sides of the neck, and the vascular arches to which they lead, are 
most distinctly visible, is, in the egg of the common fowl, about the 
third or fourth day of sitting; in the embryo of the Swine, about three 
weeks after impregnation ; and in the human subject, about the fifth week 
of gestation. 
The next paper, following our usual order of reference, relates to a 
* Schadel-und Kopf-mangel an Embryonen von Schweinen,”’ and contains 
