28 ANDERSSON, COMPARISON OF COTTUS POECILOPUS WITH COTTUS GOBIO. 
males and higher in C. gobio. OC. poecilopus here again seems 
to retain the juvenile or the female state. 
From the preceding description of the unpaired fins and 
of their scale of development it appears that the bases of all 
the three fins increase in length with age and that they are 
longer in C. poecilopus, which thus in this respect represents 
the more developed stage. Moreover, the two dorsal fins be- 
come lower with increasing age and are lower in C. poeci- 
lopus, which also in this respect seems to correspond with an 
older stage of development. The anal fin on the other hand 
increases in height with age and is lower in C. poecilopus, 
which latter thus in this respect seems to remain in the 
juvenile state. j 
The fins thus seem to show that there exists another re- 
lation between the forms beside the one which was shown 
by the measurements of the head and by other measurements. 
It is clear, however, that, when two forms differ from each 
other on the ground of a less development in one of them, in 
this less developed form some characters may be more highly 
developed than in the other, which latter, although generally 
more advanced in the development, in this respect remains in 
a more primitive stage. 
Applying in this respect the bio-genetic law: »The onto- 
geny recapitulates the phylogeny» one may accept that in 
the primitive form the dorsal fins were short and high and 
the anal fin also short but low. Looking on the marine 
Cotti, from which the fresh-water species probably are a de- 
parture, we also find these to have high dorsal fins and a 
comparatively low anal fin. According to Professor SMITT's 
measurements of C. scorpius, C. bubalis, and C. Lilljeborgii 
in the second edition of »Scand. Fishes>, in these at least the 
base of the second dorsal and that of the anal fin are shorter 
than in the fresh-water Cotti. We may then accept that 
their living in fresh water caused a lessening of the height 
of the dorsal fins, caused perhaps in some degree by their 
manner of life, — in crevices, under stones, and in such 
places, where high fins would have been inconvenient. In 
exchange, these fins increased in length as did the anal fin 
also. As the anal fin, however, was rather low already in 
the primitive stage, there was no reduction in the height of 
this fin. C. poecilopus has in these changes farther advanced 
