24 ANDERSSON, COMPARISON OF COTTUS POECILOPUS WITH COTTUS GOBIO. 
a common Cottoid character, and there has been no reason 
since for a diminution of the mouth in either of the branches. 
. 
The depth of the body. 
| 
C. poecilopus. | C. gobio. | 
| 
[| 45,21 57,5| 76,1] 42,5] 57,9] 75,5 | 
19 | 43,4] 62,7) 76,1| 42,41 58 | 75,81 
7 
Greatest depth of the body in 2 of the || 14,0| 15,3 16,3| 14,4! 15,9 15,9| 
length fot tRe "POy. > fs. feb re läge i | 
Length of the body in millimetres. . . . 
19 | 14,7| 16,3| 15,4] 15,3] 15,1] 15,7 
| Smallest depth of the body in 2 of the (3) 4,5) 4,9] 5,21 5,5) 6,11 6,0 
lenosth "01 fe DOCY så ga ense. ch söka re 3 || 
en GR 19! 4,7) 4,9) 4,9) 5,5) 5,7) 5,7) 
The greatest depth of the body (at the beginning of the 
first dorsal fin) is, as is shown above, nearly the same in the 
two forms, or even a little greater in the fullgrown males of 
C. poecilopus than in corresponding specimens of OC. gobio.! 
The depth increases with age in all cases, but the difference 
due to age is as usual less in the females than in the males. 
On the otber hand, if we look at the smallest depth ot 
the body (that of the tail), we again find the same circum- 
stance there as in the head. A gradual increase in the depth 
of the tail appears from the youngest specimens of C. poeci- 
lopus to the oldest ones of C. gobio. The tail is also deeper 
in the males, wherefore C. gobio as usual represents the more 
developed stage or the male-stage. 
The unpaired fins. 
When measuring the length, that is the base, of these 
fins, one can take the measurements in two different ways; 
from the first ray to the last or from the first ray to the 
end of the thin appendage, more or less developed, which is 
a continuation backwards of the fin-membrane. In the anal 
fin this is usually of no great size, for which reason I have 
! The extraordinary percentage which is found in the middle-sized fe- 
males of C. poecilopus may be owing to the fact that in this group, which 
numbered only six specimens, there were two very deep ones (one distended 
by large ova), which naturally amongst so few specimens caused an increase 
of the normal average. 
