PLANKTONIC STUDIES. 603 



of light.'' Microscopical investigation of tho water showed that the 

 luminous animals were for the most part small Crustacea {Ostracoda), 

 to a less extent Medusa', Salpw, worms," etc. (25, pp. 42, 372). Chierchia, 

 three years later, in the same region and in the same mouth, saw the 

 same brilliant pheuomeuou: "The most brilliant emerald-green light 

 was produced by an infinitude of ostracods*' (S, p, 108). 



Schizopoda. — Not less important in the planktonic life than the ostra- 

 cods (sometimes even more important) are the schizopods. They also 

 occur in wide stretches in immense swarms at the surface, as well as 

 in greater and lesser depths. They also play a great role in the cycle of 

 matter in the sea {Stoffa^echsel des Meeres); on the one side since tiiey 

 devour great quantities of i^rotozoa and i)lanktonic larv;e, and on the 

 other because they serve as food for the cephalopods and fishes. Many 

 schizopods, like many ostracods and copepods, belong to the most bril- 

 liantly luminous animals, and, like the latter, furnish very interesting 

 problems for the bathygraphy of the plankton. G. O. Sars, w^ho has 

 worked up the rich material collected by the (Jhallen(/er, di.stinguished 57 

 species, and found that 32 of these lived only at the surface, G from 32 to 

 300 fathoms, and 4 extended down below 2,000 fathoms (as far as 2,740 

 fathoms), (G, p. 730), Chnn also has discovered in the Mediterranean a 

 number of new zonary and bathybic schizopods very different from the 

 pelagic varieties of the surface, Sfylochiron, A rachHomysis, etc. (15, p. 30). 



The phyllopods {Daphnida'), the amphipods {Phronimidw, Hyperi- 

 dw), and the decapods {Miersida', Sergestidw) are indeed represented 

 in the plankton by a number of interesting forms, partly oceanic, 

 l^artly neritic; and some of these occasionally appear in considerable 

 quantities. But as a whole they are of fjir less importance than the 

 copepods, ostracods, and schizopods. The same applies also to the 

 other groups of Crustacea, although many of them in their larval state 

 take a great part in the constitution of the plankton. Also in regard 

 to these multiformed and often nhujidaiit jjelagic crustacean larva', us 

 well as for the mature crustacean animals, the advancing plankton 

 study has still to establish and explain a fund of facts; namely, in 

 relation to their pelagic, zonary, and bathybic distribution; their migra- 

 tions, and the relations in which this planktonic fauna stands to the 

 benthic fauna. 



Iiisecta. — That im^jortant branch the Tracheata, the most numerous 

 in forms of all the principal divisions of the animal kingdom, has in the 

 sea no representatives whatever. The Protracheata, Myriapoda, and 

 Arachnidf ai-e exclusively inhabitants of the land and in small part of 

 the fresh water, except the pycnogonids or pantopods (in case these 

 really belong to the Arachnida'). Among the Tnsecfa there is only a 

 single small group of true marine animals, tho family of the Halobatida'. 

 These small insects, belonging to the Hemiptera, have completely ac- 

 (piired a ])elagic mode of life, and run about in the tropical ocean just 

 as our "water-runner" (Hydrometra) on the surface of fresh water. 



