42 
POPULAR SCIENCE REVIEW. 
the Batrachia, is to be found in the presence of external 
branchial organs in the embryos of Sharks and Bays, and in the 
young of certain Ganoid fishes, especially of Protopterus , the 
African Mudfish. These branchiae, as in the Tadpoles of frogs 
and newts, disappear in the further development of the fishes, 
the last named of which, in many respects, seems to lead from 
the true fishes towards the Batrachians. 
But although we cannot say that an actual metamorphosis 
occurs in any other fishes, it has long been known that changes do 
take place in some of them, and that in many cases the young fishes 
differ very considerably from the adults. It is only of late years, 
however, that any conception has been arrived at of the extent 
to which these changes may attain ; and it is mainly to Dr. 
Gunther, the keeper of the Zoological Department in the 
British Museum, and to Dr. Lutken of Copenhagen, that we 
are indebted for the knowledge of the changes of form occurring 
in fishes that we now possess ; the former gentleman having 
described numerous instances in various memoirs published 
during the last twelve years ; and the latter being the author of 
several scattered papers on the subject, and quite recently of a 
valuable memoir on the changes observable in fishes of the 
Atlantic,* in which he has summed up and illustrated many of 
his own and Dr. Gunther’s results. Dr. Lutken proposes to deno- 
minate these changes of form 4 hemimetamorphoses.’ Dr. Gunther 
has also devoted a chapter in his recently published and admir- 
able Introduction to the Study of Fishes to a general consideration 
of these phenomena. 
Without figures, both of the different young forms and of 
the adult fishes, it is of course, in many cases, impossible to 
convey an intelligible idea of the changes which have been 
brought to light by the investigations above referred to, but we 
will endeavour to describe two or three of them so as to enable 
the reader to see the bearing and importance of such results as 
have been, or may be, obtained in this field of research. 
The occurrence of important changes in the so-called ‘ Flat 
fishes ’ ( Pleuronectoidei ) has long been known, but as they are 
very curious we may devote a few words to them here. These 
fishes, of which the turbot, the plaice, and the sole, are well- 
known examples, always have the body broad and much com- 
pressed from side to side ; they live upon the bottom, where 
they are in the habit of lying quietly, and the two sides of the 
body are differently coloured, — that which is kept habitually 
downwards and applied to the ground in repose being of a white 
* 1 Spolia A tlantica/ in Kongl. Danshe Vidensk. Selshabs Skrifter , 
frth series. 1680. This Memoir is in Danish, but the author has appended 
to it a r£sum6 in French, a translation of which will appear in the Annals 
and Magazine of Natural History, 
