Nova Acta AcademicB Naturce 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 hranchim 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 



