﻿COPEPODA 65 



As the Due d'Orleans is the expedition which has made tlie most systematic plancton-iii- 

 vestigations from different depths witli measurements of sahnity and temperature, and as Koefoed 

 and Da mas are the only ones, who have separated the three types, I tliink a more detailed survey 

 of their material, sliould pay. 



Ps. major, which was first recorded by G. O. >Sars north of the New Siberean Islands, was 

 only taken a single time 78°o5 Lat. N. 5°2i Ivong. W. ''y? 1905 between Soo and 1350 met. (salinity 

 34'95 7oo; temp. o-o8° ^-o•37" Cels.). 



Ps. cloigatiis was only taken near the coast of Spitzbergen (c. 80° Lat. North i4''33 I/Ong. East) 

 at 4 stations near the surface (Temp. 0-50 — 2'5o " C.) and at the mentioned stations near Ivxst Greenland. 



Ps. gracilis, which has previously been recorded by Sars at the coast of Finmarkeu and be- 

 tween Fiumarken and B;ireu Island "a ete capture cutre 600 metres et la sin-face; il est particuliere- 

 ment abondant au-dessus de 200 metres; d'apres les estimations faites par Koefoed, 11 parait nioins 

 frequent le long de la cote groulaudaise qu' an large, mais il est tres frequent taut dans le Gidfstream 

 que dans le courant polaire". The species is generally missiug in hauls from o — 20 meter.s, but it has 

 been found common here at a few station (c) independent of the time of the day and of the temperature 

 (lying between -^ 170 and + i'50). It has been found common at a depth between 480 and 600 metres, 

 juuiores between 800 — 1000 metres (p. 270), and abundant at temperatures from -=- 170 to ;- 3" C. Tlie 

 salinity, at which it is found common, varies from 30-60 °/,x, to 34-90 °/oo- 



As set forth by F'arran the conditions at which this species can flourish are very varied. 

 The salinity varies from 7-25 "/qo to 35-30 %o, the temperature from -^ 1-70° C. to 12-47° C, 't is found 

 from the surface near the coast, where it is often left in tidal pools, as deep as 600 metres in the 

 open ocean. About the details of its biology I refer to Farrau, several interesting studies of Herd- 

 manu from the Irish Channel but especially to Kraeeft, who in the I'altic and the North Sea has 

 studied the growths and the occurrence at different depths of the various stages (juuiores). He writes 

 (1910 p. 79) "es zeigt sich deutlich da.sz das III Stadium von vSchicht zu vSchicht, von Boden nach der 

 Oberflache gerechnet in immer groszer werdenden Meuge vorhauden ist"; he found that mature females 

 (April 1906 in the Baltic) were present in 59-1 % between 75 and 30 metres, but only in 3-1 ^Vo between 

 5 and o metres. 



About the time of propagating I have in the literature only found that the Due d'Orleans has 

 collected mature females and males (Vy 1905 8o°i3 Lat. N. 7*'42 Long. East 400—500 metres, 0-23— 0-80° C, 

 and 's/s 1905 7i°22 Lat. N. i8"58 Long. East, 200—400 metres, o-67~r53'' C). 



Remarks. It has previouslv been mentioned that no characters are found by which all spec- 

 imens could be referred to one of tlie three ty[)es of Psciiiiocnlamts iiiiiiii/iis\ in the same sample inter- 

 mediary links are found not only between the extremities of the mature females but also between 

 the copepodites of stage IV — V, in which however the difference between the types is less marked. 

 The question how to explain marked differences in size and other characters found in llie same sample 

 under the .same biological conditions, if they all lieioug to the .same species, is too vexed to be an.s- 

 wered now. Specificuess of the different t\pcs ma\- jierhaps be excluded by the examination of several 

 hundreds of specimens at least, from sanqjles with marked variation between the specimens, after 

 Gal ton's statistical methods. 



Th,: liifjolf Hx|ii-,mi..ii, III. ,|. 9 



