COPEPODA 65 



As the Due d' Or leans is the expedition which has made the most systematic plancton-in- 

 vestigations from different depths with measurements of salinity and temperature, and as Koefoed 

 and Dam as are the only ones, who have separated the three types, I think a more detailed survey 

 of their material, should pay. 



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

 only taken a single time 78O5 Lat. N. 52i Long. W. l6 / 7 1905 between 800 and 1350 met (salinity 

 34'95%o; temp. 0-08 -f- 0-37 Cels.). 



Ps. elongatus was only taken near the coast of Spitzbergen (c. 80 Lat, North i433 Long. East) 

 at 4 stations near the surface (Temp. 0-50 2-50 C.) and at the mentioned stations near East Greenland. 



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

 tween Finmarken and Baren Island "a etc capture entre 600 metres et la surface; il est particuliere- 

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

 frequent le long de la cote gronlandaise qu' au large, mais il est tres frequent tant dans le Gulfstream 

 que dans le courant polaire". The species is generally missing in hauls from o 20 meters, 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'5o). It has been found common at a depth between 480 and 600 metres, 

 juniores between 800 1000 metres (p. 270), and abundant at temperatures from -f- 170 to -f- 3 C. The 

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



As set forth by Far ran the conditions at which this species can flourish are very varied. 

 The salinity varies from 7-25 %<> to 3530 %o, the temperature from -=- 170 C. to I2'47 C., it 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 Farran, several interesting studies of Herd- 

 niann from the Irish Channel but especially to Kraeeft, who in the Baltic and the North Sea has 

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

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

 Oberflache gerechnet in immer groszer werdenden Menge vorhanden 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 % 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 ( 8 / 7 1905 8oi3 Lat. N. 7^2 Long. East 400500 metres, 0-23 0-80 C., 

 and '5/ 8 1905 7i22 Lat. N. i858 Long. East, 200400 metres, 0-67 1-53 C). 



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

 imens could be referred to one of the three types of Pseudocalanus mi-nutus; 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 the same sample 

 under the same biological conditions, if they all belong to the same species, is too vexed to be ans- 

 wered now. Specificness of the different types may perhaps be excluded by the examination of several 

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

 Gallon's statistical methods. 



The Ingolf-Expcdition. III. 4. o 



