6 ; G. HERBERT FOWLER. 
I1L—DISTRIBUTION. 
The occurrence of these species in really polar waters is of considerable interest. 
The record of Avohnia hamata as a truly “ bipolar” species is thus completed ; 
it ranges from 81° 30! N. (Rémer and Schaudinn) to 77° 49'S. ; it is both epiplanktonic 
and mesoplanktonic at high latitudes with low surface temperatures, but in tropical and 
warm temperate seas is known only from the colder strata of the mesoplankton. 
While, horizontally speaking 
o>? 
it appears to be cosmopolitan, and is fairly eurythermal, 
it has not been recorded definitively from a higher temperature than 12°7° Cent. 
(‘ Challenger’ Collection). 
As to Sagitta hevaptera, the captures of both ‘ Discovery’ and ‘Challenger ’ 
complete its record as a ‘‘ pantothermal”’ species, that is to say, one living at practically 
every known sea-temperature, from about 29°C. to — 2° C. ; and asa truly cosmopolitan 
species, ranging from Spitsbergen in the north to the ‘Discovery's’ winter quarters 
in the south, and from every sea from which Chaetognatha have been recorded. 
Sagitta serratodentata, on the other hand, failed at the colder stations of both 
‘Discovery’ and ‘ Challenger’ ; its minimum record f has now been reduced to 4°6° C., 
the lowest temperature at which it had been taken previously being between 6°6° and 
12°2° C. at the Falkland Islands. Its definitive temperature limit in the Northern 
Hemisphere is at present 12°2° C., but in view of the ‘ Discovery's’ captures it may 
possibly prove to extend somewhat further north than its present record of lat. 
60° 12'N. At any rate, it seems to be clear that it is not “ bipolar,” although 
subantaretic and north-temperate. 
The southern captures of hevaptera, serratodentata, and hamata, from all-sourees, | 
have been plotted on the appended circumpolar chart, together with the mean annual 
surface isotherms of 12° and 6° C., as calculated by Dr. Schott. The former appears 
to indicate approximately the northerly limit of hamata as an epiplanktonic form, the 
latter similarly to indicate the southerly limit of serratodentata. 
The definitive temperature limits given in the ‘Siboga’ Report already cited 
require amendment as follows :—hevaptera, lowest temperature, — 2° C. ; serratodentata, 
lowest temperature, 4°6° C.; hamata, highest surface temperature, 12°7° C., lowest 
temperature, — 2° C. 
+ This record is, however, of a single specimen, and the species had failed at the two previous stations 
(compare p. 8 above). It is therefore possible that we are dealing merely with an isolated specimen, which had 
drifted beyond its natural limits. 
