32 ANDERSSON, COMPARISON OF COTTUS POECILOPUS WITH COTTUS GOBIO. 
form probably, as well as in most of the marine Cotti, there 
existed a distinct difference in sex, the fins in the older males 
being elongated, the fins in the older females short.1 This 
sexual character is still very distinct in OC. poecilopus, show- 
ing here in this respect a primitive stage. In CO. gobio it 
has almost entirely disappeared. 
'The innermost ray of the ventral fin. 
 C. poecilopus. | OC. gobio. 
| 
| | 
| 37 | 45,2| 57,5) 76,11 42,5) 57,9| 75,5 
" "19 | 43,4| 62,7| 76,1] 42,4| 58 |75,8 
| Length of the innermost ray in the ventral (3 6,2) 6,5) 6,81 10,91 12,8) 12,8 
fin in & of the length of the body. . .s« | 
RR RET RA 19 | 7,1) 5,9) 5,111,9| 12,8) 12,4 
Length of the innermost ray in the ventral [3 36 ol 36,7| 33,81) 63,4| 72,3| 70,7 
fin in 4 of the length of the ventral fin. j ' EN , 
; A 12 | 39,7| 32,61 28,8 67,2| 68,7) 69,31 
| Length of the body in millimetres . . 
Although the paired fins are on the whole very much 
alike in the two forms, they still furnish one of the most 
important characters distinguishing the two forms. The dif- 
ferent length of the innermost ventral ray has already been 
spoken of above. Not its length alone, however, but the 
course of its development, especially, shows that the two 
forms are in this respect distinctly different. Comparing the 
length of this ray with that of the fin, we find it not only 
very much longer in C. gobio, but also increasing noticeably 
with age, in the males at least, while, on the other hand, in 
C. poecilopus this ray decreases in length with age, especially 
in the females. If it be compared with the length of the 
body, the case is somewhat different; we find then that the 
ray slightly increases in length even in the male of C. poeci- 
lopus. This difference is due to the rapid growth of the fins 
in the older males of this form, which causes the small in- 
crease in the length of the ray to appear to be a diminution 
of it in comparison with the fin. 
1 Prof. SMmitT's measurements of C. bubalis in »>Scand. Fishes> show 
that the fins of this fish increase with age in the males, but that they de- 
crease in the females. 
