26 ANDERSSON, COMPARISON OF COTTUS POECILOPUS WITH COTTUS GOBIO. 
to the largest C. poecilopus. Consequently, C. gobio repre- 
sents in this case the juvenile stage. 
In counting the rays in the fin we find on an average 
a larger number in C. poecilopus than in C. gobio. In the 
former they vary between 7 and 9, in the latter between 6 
and 9. The following table shows the number of rays in the 
specimens examined. 
Out of 68 (34 >, 34 2) examined | Out of 58 (38 >, 20 2) examined 
gobio specimens | poecilopus specimens 
ii ade AV LASER I ye 6 rays 5 (4.37,1 2) hadvbel silaumaya 
dl (20 STAD) HA Vv cr 36 (22.07, d4 PP), 2 förd OE 
1Tvattker 104P) anat RB Ft IOFS 2 wt, ORBIÄA 
ZH den) SAPA ST ÖS 
The second dorsal fin shows a slight difference from the 
first. The appendant membrane is so well developed in this 
fin of C. gobio that if it be counted in the measurements the 
second dorsal appears longer in C. gobio than in C. poeci- 
lopus. If it be not counted in and the length of the fin be 
measured from the first to the last ray only, we find the fin 
somewhat longer in OC. poecilopus, which here also, though 
less distinctly so, represents the adult stage. No difference 
in sex appears in this respect, at least in fullgrown speci- 
mens, but if the fin be measured in the other way, then it 
is found to be longer in the male, in which the appendant 
membrane is more developed than in the female. 
Examining more closely the measurements of the length 
of the fin, taken from the first to the last ray, it seems to 
follow no certain rule in its development. In the males of 
both forms we find that the fin, after having increased in 
length, reverts slightly by a kind of reaction to the juvenile 
state. A similar state of things appears in the female of 
C. poecilopus, while in that of C. gobio the fin is very long 
in the smaller specimens, becomes shorter in the middle-sized 
ones, to again increase in length in the largest ones. Also 
in this fin of C. poecilopus there are a larger number of 
rays than in that of C. gobio, though the difference is less 
than in the first dorsal fin. The number of the rays in 
C. gobio varies between 15 and 18; in OC. poecilopus between 
16 and 19. 
