PLANKTONIC STUDIES. . 603 
of light.” Microscopical investigation of the water showed that the 
Juminous animals were for the most part small Crustacea (Ostracoda), 
to a less extent Meduse, Salpe, worms,” ete. (25, pp. 42, 372). Shierchia, 
three years later, in the same region and in the same month, saw the 
same brilliant phenomenon: “The most brilliant emerald-green light 
was produced by an infinitude of ostracods” (8, p. 108). 
Schizopoda.—Not less important in the planktonic life than the ostra- 
cods (sometimes even more important) are the schizopods. They also 
oceur 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 (Stoffwechsel des Meeres); on the one side since they 
devour great quantities of protozoa and planktonic larvee, 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, who has 
worked up the rich material collected by the Ch allenger, distinguished 57 
species, and found that 32 of these lived only at the surface, 6 from 32 to 
300 fathoms, and 4 extended down below 2,000 fathoms (as far as 2,740 
fathoms), (6, p. 739). Chun also has discovered in the Mediterranean a 
number of new zonary and bathybie schizopods very different from the 
pelagic varieties of the surface, Stylochiron, Arachnomysis, ete. (15, p.30). 
The phyllopods (Daphnide), the amphipods (Phronimide, Hypert- 
de), and the decapods (Mierside, Sergestide) are indeed represented 
in the plankton by a number of interesting forms, partly oceanic, 
partly neritic; and some of these occasionally appear in considerable 
quantities. But as a whole they are of far 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 abundant pelagic crustacean larve, as 
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. . 
Insecta.—That important 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 
Arachnide are 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 Arachnid). Among the Insecta there is only a 
single small group of true marine animals, tho family of the Halobatide. 
These small insects, belonging to the Hemiptera, have completely ac- 
quired a pelagic mode of life, and run about in the tropical ocean just 
as our “water-runner” (Hydrometra) on the surface of fresh water. 
