PLANKTON OF THE GULF OF MAINE 



163 



Large ones, however, especially the females with eggs, have rarely been taken in 

 our surface nets; and even medium-sized individuals have usually been but sparsely 

 represented in the surface hauls, although we have occasionally met exceptions to 

 this rule, notably in the northeastern part of the gulf during August in 1912 and 

 1913 (stations 10032 and 10096) and off Marthas Vineyard on July 10, 1913 (station 

 10002). On the other hand, E. compressa, like Calanus, has usually proved more 

 abundant above than below 100 meters depth whenever two or more subsurface hauls 

 have been made at different levels. 



The bathymetric distribution of the larvae of Euthemisto differs from that of 

 the adults, for they are usually most numerous at or close to the surface. The 

 fact that we have taken them in swarms in the surface nets at several stations where 

 their parents (or at least females with eggs) were plentiful at deeper levels is evidence 

 that they rise through the water immediately after they are hatched — one of the 

 innumerable provisions of nature for the perpetuation of the species, for otherwise 

 they would inevitably be devoured by their own voracious progenitors (p. 107). 

 Examples of a bathymetric stratification of this sort as between adults and larvae 

 were noted in the eastern part of the gulf (stations 10092 and 10093) and off Marthas 

 Vineyard (station 10112) in August, 1913; over Georges Bank in July, 1914 (sta- 

 tions 10215 and 10219); off Shelburne in June; in the western basin in August, 

 1915 (stations 10293 and 10307); and off Marthas Vineyard in July, 1916 (station 

 10353). 



Both species of Euthemisto — compressa and bispinosa — like Calanus finmarchicus 

 and Sagitta elegans, tolerate very wide fluctuations of temperature and salinity, as, 

 indeed, they do in European waters as well (Tesch, 1911). So far as actual occur- 

 rence goes, we have taken them over the whole range of temperature prevailing 

 within the limits of the gulf, from the icy waters of winter and of the Nova 

 Scotian current, on the one hand, to the summer-heated surface of the western 

 basin and the warm waters along the outer edge of the offshore banks, on the other; 

 likewise over the entire range of salinity proper to the open waters of the gulf, except 

 for the very lowest. It is not possible to draw any close parallel between the abund- 

 ance (or reverse) of Euthemisto and the temperature from the data so far obtained, 

 but we have never found it abundant in the coldest season, and most of the rich 

 catches have been made in temperatures warmer than 5°, as appears from the follow- 

 ing list of the readings at and above the levels at which the horizontal parts of the 

 hauls were made, at several stations productive in large Euthemisto. 



' Surface. 



