34 ANDERSSON, COMPARISON OF COTTUS POECILOPUS WITH COTTUS GOBIO. 
and with that of the anterior part of the body. The above 
table of averages shows therefore that a great correspondence 
exists between these measurements and those of the head. 
There appears a more or less regular increase from the young- 
est specimens of C. poecilopus to the oldest ones of C. gobio. 
The table also shows that the measurement is greater in the 
poecilopus male than in the female. &C. gobio thus in this 
respect, as in that of the head, represents the adult or the 
male stage, while C. poecilopus retains the juvenile or the 
female stage. 
As shown in the table above, the difference between the 
forms is less marked in the distance of the posterior dorsal 
fin from the tip of the snout than in that of the anterior 
one, which is explained by the fact that this measurement 
depends also on the length of the first dorsal, mentioned 
above, which, contrarily to the measurement in question, is 
more developed in C. poecilopus, and thus causes a diminu- 
tion of the comparatively great difference which otherwise 
would be found in this measurement, as in that of the dis- 
tance of the first dorsal. 
The distance between the insertion of the ventral fins and 
the tip of the snout. 
| OC. poecilopus OC. gobio. 
7,51 70,11 42,51 5 
41 62,7| 76.1) 42,41 58 | 75,8 
2,8 23,5| 23 |23,6| 24,2 
3,3) 24,2] 23.3) 24.1) 24,6 
Length of the body in millimetres . . . .«< 
Distance of the ventral fins from the EN 
of the snout in 4 of the length of the body 
Ooh 9 Ö 
The distance of the ventral fins from the tip of the snout 
increases in both forms and in both sexes and is greater in 
C. gobio than in C. poecilopus, everything being in corre- 
spondence to the course of development of the anterior part 
of the body spoken of above. We find, however, another re- 
lation between the sexes. In the females of the two forms 
this distance is somewhat greater than in the males of the 
same size, which is a sexual difference found in all the mea- 
surements of the ventral part; at least in C. gobio, being 
