12 THÉEL, PRIAPULIDS AND SIPUNCULIDS OF THE SWEDISH ANTARCTIC EXPEDITION 1901 — 1903. 



With regard to the above quotation Murray says: »It has been estimated 

 that the bottom of the ocean in this region must at the time have been covered to 

 the depth of about six feet with the dead bodies of the tile-fish and other marine 

 organisms, and it seems evident, from the subsequent researches of Prof. Libbey, 

 that their destruction was due to the lateral shifting of currents from different 

 sources and of different temperatures, thus producing a wide range of temperature 

 even at depths of 50 and 100 fathoms.» Seeing that the surface and under-currents, 

 when they meet, have the pover to exercise such ruinous influence över such vigorous 

 forms as adult specimens of Cephalopods and fishes, then there is very little chance 

 that the very susceptible larvre of Evertebrates can sustain the violent struggle for 

 existence in the open sea. 



Besides, other facts confirm the accuracy of my views. For, supposing that 

 larvee of shallow-water animals really could endure the struggle for existence under 

 such perilous and permanent transport by means of unknown and dubious currents 

 from polar-circle to polar-circle, then the consequence must be that a very great 

 number of fully identical species must be met with in the two polar regions. But 

 this is by no means the case. A careful investigation will certainly show that only 

 a very limited number of fully identical species is to be found in the two polar seas. 



In this connection, another question of highest importance calls for treatment, 

 and, if possible, solution. How long does a larva of a shallow-water animal Ii ve in 

 the open sea without being forced to sink and settle on the bottom? This question 

 is indeed very difficult to answer. According to my practical experience a larva of 

 a sea-urchin goes through its plankton stages during a period of 6 to 8 weeks, varying 

 in accordance to the temperature and the supply of food. In other marine inverte- 

 brates the floating stage is gone through more quickly and in many instances this 

 development does not require more than a few days. 



The fourth question, concerning the direction and rapidity of the sea-currents 

 seems to be very difficult to answer conclusively. Even a professional hyrographer 

 appears to be in doubt as to the true nature of the deep-water currents. For my 

 part, I admit frankly that my studies have not been such as to warrant me in giving 

 a view of my own on these contested matters. Consequently I must confine myself 

 to giving the opinions of some eminent authorities. 



In 1911 Krummel 1 pronounces his opinion on the deep-water currents in the 

 following manner: »Was die directen Strommessungen betrifft, so ist der Stånd un- 

 serer Kenntnisse der die tieferen Schichten beherrschenden Strombewegungen zurzeit 

 noch bedauernswert riickständig; . . . Ein wenig giinstiger steht es um eine theoretische 

 Beurteilung der Notwendigkeit gewisser stromartiger Wasserversetzungen in den mitt- 

 leren und unteren Schichten; doch stellt sich auch hier die nicht genau zu beklagende 

 Unzuverlässigkeit der älteren Bestimmungen des Salzgehalts dieser Tiefenschichten 

 hinderlich in den Weg. ...» 



Thus Krummel states that our present knowledge of the deep-water and under 

 currents in general is unsatisfactory. 



1 llaudbuch der Occanographic. lid. II. Stuttgart 1911, p. (i 13. 



