89 SECTIONAL ADDRESSES. 
widely separated localities formed one community and came together 
in one breeding-place. To test the soundness of this conclusion he in- 
vestigated Zoarces, a fish of about the same shape and with about the same 
number of vertebre as the eel, but viviparous, and not migrating for breed- 
ing. He found that samples of Zoarces from various parts of the Kattegat 
and Baltic differed slightly, but generally had an average of about 118 
vertebre, but that in the shallow Danish fiords the number was less, and 
decreased progressively the farther the distance from the sea. Conditions 
of temperature, salinity, &c., are very different in the different fiords, 
50;— 
set rae) 109-3 i10.2-| a ~ 
46 IN fh 
er IN Bhik 
“CCEA we 
H Bei 
ASEH 
See ane colts 
1c 
iI 
ul 
| 
———— os 
SS eS 
iaasaees 
—| 
ea 
a 
* AC 
Pammaurield rhea AEE 
is | IEA] lie 
= Ban wis HH 
seared geitiece 
i SCH E 
NUMBER OF INDIVIDUALS 
N 
a 
2 EEE AIEEE 
: Hf NU TALIA 
: | | AAMT TZ \ 
PANES 
a annn SCE REES 
1034 56 7 8 9 HON 12 13 i4 15 16 17 18 19 12021 22 
NUMBER OF VERTEBRA 
Graphic representation of number of vertebre in samples of Zoarces viviparus from 
(1) Kattegat, 5 miles north of Mariager Fiord (average 117°4); (2) Mouth of 
Mariager Fiord (average 115-4); (3) Mariager Fiord, 7 miles from the mouth (average 
111); (4) 15 miles from the mouth (average 110-2); (5) 16 and 20 miles from mouth 
(two similar samples, average of each 109-3). The wide range and irregularity of the 
curves for the intermediate populations are noteworthy. 
and I am inclined to think that the critical character common to all of them 
is that they give the Zoarces an opportunity of leading a quiet life amidst 
a plentiful supply of food ; hence the fiord Zoarces can be distinguished at 
a glance from those outside by their shorter and deeper form. In the 
Mariager Fiord, a narrow inlet about twenty miles long, the average number 
of vertebree decreases from 115 at the mouth to 111 about seven miles 
inland and 110 about fifteen miles inland ; two samples from the extreme 
end_of the fiord and from a point four miles from the end both showed 
exactly the same average, 109.3. In the Roskilde Fiord, a very large 
