576 DR. G. it. FOWLER ON THE [June 21, 



method is theoretically excellent *, but is not certain enough for 

 use as an argument against the negative observations of the ' Blake ' 

 and 'Albatross.' 



While I am fully in agreement with Professor Chun's results, it 

 must be admitted that the original pattern of his net was not 

 devoid of sources of error, which Agassiz was not slow to point 

 out. Chun reported 2 an abundant fauna from all depths in the 

 Mediterranean, but, this being a warm closed sea with a uniform 

 temperature of 55 or 56 E. from. 100 down to 2400 fathoms and 

 more, no thermal barriers are here set to the vertical descent of an 

 organism. It is not therefore possible to argue from this case to 

 that of the great oceans, the temperature of which decreases with 

 the depth until 30 F. or even less is reached. 



Three hauls made by Prof. Chun on a voyage to the Canary 

 Islands 3 revealed a Mesoplankton at great depths, the general 

 character of which agreed with the similar captures of the ' Chal- 

 lenger ' and ' National. ' The net used was an improvement on 

 the Mediterranean pattern: open nets were also employed in 

 other hauls. 



As regards the ' National ' net, a modification of Chun's pattern, 

 Prof. Agassiz expressed suspicion of the locking arrangement which 

 closed it. Prof. Brandt was kind enough to show it to me some 

 years ago in Kiel ; it is extremely ingenious in mechanism, but, as 

 Prof. Hensen 4 admits, it is most uncertain in its action ; and, if I 

 may judge from my own experience of a screw-propeller, it would 

 not give very exact information of the depth ; for the rate at which 

 the propeller travels (i. e. the time-intervals from first hauling to 

 opening, and from opening to shutting) varies so much with the 

 rate of the steam-winch (an inconstant) and with the rolling of the 

 ship. If there is any swell, the strain on the line as the ship rolls 

 to leeward sends the propeller round at a greatly increased rate. 

 While, however, venturing to criticize the method, I accept the 

 positive results without any reserve, so far as they are published. 

 They have been most recently summarized by Prof. Brandt 5 , and 

 show a mesoplanktonic fauna which rapidly diminishes in numbers 

 below 100 fathoms, together with a large number of dead organ- 

 isms which are slowly settling to the bottom. Prof. Hensen 6 



1 Though theoretically perfect and simple, this method of investigating Meso- 

 plankton appears to me to present two practical objections to its use : the one, 

 that such an enormous amount of material must be collected as will take years 

 for its proper identificaiton, before a comparison of surface and deep nets can 

 be instituted ; the other, that much of the deep material must inevitably be 

 reduced to soup by pressure against the open tow-net in its long passage upwards ; 

 only forms with a strong skeleton (Eadiolaria, Copepoda, &c.) can be expected 

 to arrive fairly unbroken. In a closed net the resistance of the water does not 

 appear to press the contents of the net against the meshes in the same way. 



2 0. Chun: Bibliotheca Zoologica, i. 



3 C. Chun: Bibliotheca Zoologica, vii., and SB. Akad. Belin, 1889, p. 519. 



4 V. Hensen, Ergebn. d. Plankton Expedition, MethodikderTJntersuchungen, 

 p. 106. 



5 K. Brandt : Verb.. Gesellsch. deutschen Naturforscher und Aertze fiir 

 1895, Liibeck, p. 107. 



6 V. Hensen : Keisebeschreibung der Plankton Expedition, p. 28. 



