THE GERMAN CARP IN THE UNITED STATES. 533 
It seems probable, however, that the character of the scales should 
be placed with the other four categories of characters given above 
as being another modification brought about by artificial breeding and 
selection and not as a condition due simply to conditions of domesti- 
cation, as is sometimes supposed. All of these characters are probably 
heritable, although some of them, such as rate of growth and time of 
sexual maturity, may undoubtedly be readily influenced by external 
conditions in the individuals of a single generation. Furthermore, 
there apparently can be all combinations of these characters, and the 
so-called different varieties and races are the fish possessing the vari- 
ous combinations. In general, it may be said that the most highly 
specialized carp are those which are destitute of scales, which grow 
quickly, are high in proportion to their length, and tend to have a hump 
back of the head, and which become sexually mature at an early age. 
These various forms of carp probably differ in no essential way, 
except that they are not so well differentiated and established, from 
what are spoken of as ‘‘breeds” by stock breeders. There would 
appear to be no valid reason for calling those with the different char- 
acter of scales ‘‘ varieties,” and to class those which are differentiated 
as to form as ‘‘races.” It is merely that the most obvious characters 
are these which haye become most permanently established by selec- 
tion, namely, character of scales first and form second. Walter 
claims that ability for quick growth has also been fixed in certain 
stocks. Thus a fish of good quick-growing stock may later make a 
good growth even if poorly nourished during its first or second year, 
whereas a fish of poor stock under similar conditions would be perma- 
nently stunted. The hardiness, or ability to resist climatic condi- 
tions, he says has not yet been made permanent in any stock, though 
it is claimed that scale carp possess the ability to a greater degree than 
the others. The adaptability to climatic conditions probably becomes 
reduced rather than increased as the other characters are developed. 
All intermediate stages are found in the sets of characters men- 
tioned. For example, fish may be entirely covered with scales, but 
the scales are larger and fewer in number than on the regular scale 
carp, and, similarly, one finds all gradations between the leather and 
the mirror carp. The same thing is true of the form of the body. 
This is especially the case with the fish in our waters, where all kinds 
have become established and have interbred until there is a complete 
series in the gradation of characters in almost any lot of fish taken, 
and a division of them into varieties must be an arbitrary one. Asa 
matter of convenience in my work, those fish which had larger and 
fewer scales than typical scale carp I called mirror carp. Some 
authors state that the leather carp should be entirely destitute of scales; 
others that it may have a row of scales along the back and a row on 
each side. In no case in the Great Lakes did I see a carp entirely 
