1898.] OS THE PLANKTOX OP THE FAEEOE CHAXNEL. 567 



6. Contributions to our Knowledge of the Plankton of the 

 Faeroe Channel. — No. VI.^ Description of a new Mid- 

 water Tow-net. Discussion of the Mid-water Fauna 

 (Mesoplankton) . Notes on Doliolum tritonis and 

 D. nationalis, and on Parathemisto abyssorum. By G. 

 Herbert Fowler, B.A., Ph.D., Assistant Professor of 

 Zoology, University College, London. 



[Received June 18, 1898.] 



In the first paper of this series, I proposed to leave the de- 

 scription of the mid-water nets used, and the discussion of the 

 general question of the existence of a mid-water fauna or Meso- 

 plankton, until the collections made ou the 'Research' had been 

 thoroughly uivestigated. The net which I used last year proved 

 so successful iu actual working, that it now seems to me better 

 to describe it at ouce for the information of other investigators, 

 who might give it a further trial ; the more so since my leisure 

 for research work is but small, and the coUections cannot be 

 completely finished for some months to come. 



It is unnecessary to describe here the numerous and varied forms 

 of apparatus which have been devised for the capture of animals at 

 known mid-water depths without admixture of the fauna from other 

 zones. References to them will be found, by those interested, 

 in the papers ol Hoyle=, H.H. the Prince of Monaco ^ and 

 Agassiz * ; since the appearance of the last-named, a full description 

 of the 'National' apparatus has been published by Hen sen ^ 

 Agassiz, in the paper cited, has subjected the earli(>r forms of net 

 to a searching criticism, with which I agree on the whole ; except 

 that of the Prince of Monaco and that of the ' National,' none 

 appear to exclude satisfactorily animals from undesirable zones. 

 Even that of the Priuce of Monaco does not appear to have 

 worked satisfactorily on the 'Pola'; and the modification of Chun's 

 net used on the ' National' was uncertain in its action ". 



When desirous to study for myself the question of a mid-water 

 fauna or Mesoplankton ', I feared that both the nets last quoted 

 were too expensive, and the ' National ' net too complicated for 

 use in such heavy seas as are generally to be found in the Paeroe 

 Channel, the only deep-water readily accessible to me. Eeturning 

 therefore to Chun's '' original ingenious design as a starting 



For Part I., see P Z. S. 1896. p. 991 ; Part II., P. Z. S. 1897, p. 523 ; Pai-t 

 III., P. Z.S. 1897, p. SU3 ; Part IV., antca, p. 540; Part V., anieu, p. 550. 



- Proc. Liverpool Biol. Soc. iii. 100. 



^ CR. Congres international de Zoologie, Paris, 1889, p. 133. 



* Bull. Mus. Comp. Zool. Harvard, xxiii. 1. 



■' Ergebnisse d. Plankton Exped. : Melhcdik der L'ntersuchungen p. 103 

 et seqq. (1895). 



'* For the explanation of this and similar new terms used here, .sc p. 545 an/e. 



' C.Chun: Bibliotheca Zoologica, i. 1 



