332 



thai Buch oozes, when found in a fossil state,* indicate deep 

 sea. The absence of clastic sedimenl maybe due to the low 

 relief of the land, which may have been worn down to base 

 level, thus allowing water of moderate depth near shore to 

 he free from detrital material. 



The term nekton, derived from theGreek vvx'»- to swim, was 

 introduced by Haeckelin 1890,f for those animals which lend 

 an actively swimming life. The group is typified bythe class 

 of fishes.:i: A torpedo-like form, terminating anteriorly in a 

 head, and perfect bilateral symmetry, are the chief character- 

 istics of these animals. A strong musculature for propul- 

 sion is commonly situated in the posterior portion of the 

 body, while appendages for balancing and steering are 

 usually present. The body is non-transparent, and a cal- 

 careous supporting skeleton is ordinarily developed. Typ- 

 ical nektonic animals of the modern sea are: the squids, 

 the fish, and the degenerate mammals, i. e.. whales, por- 

 poises, etc. 



The term benthos, from fiivOos. the depths of the sen. was 

 likewise introduced by Hyecke] in 1890. It covers those 

 organisms which inhabit the sea-bo ttom.§ 



We may divide the benthos into sedentary and vagrant 

 ( vagile) benthos, the former attached to the bottom, the lat- 

 ter moving over it. Living in such intimate relation to tin ■ 

 sea bottom, halo-benthonic organisms are to a high degree 

 dependent upon its fades, and their remains, moreover, are 

 generally entombed in the region where the}' have lived, 

 instead of being deposited anywhere, as is the case with 

 planktonic and nektonic organisms. The sedentary benthos 



♦Styliolina limestone of the Geneee. 



+ P]aiiktoiist\idie]i — to vtKTov, that which swims. 



; Fish are typical halo nektonic ami limno-nektonic animals, Geo-nektonic animals are 

 represented by flying insects, reptiles, birds, ami mammals. None of these lead a perma- 

 nently nektonic iit'e in the air, tor all return more or less frequently to the substratum. 

 Nevertheless, during their period of flight —which often is very long — they must be consid- 

 ered as nekton of the air. 



JTo speak of fluvial or limno-benthos, ami terrestrial or geo-benthos, is certainly a 

 stretching of the word beyond its original significance, but the value of the term in that 

 connection more than counterbalances the ety logical defects. The limno-benthos con- 

 tains comparatively few sedentary animals, of the classes of Protozoa, sponges, Hydrozoa, 

 and Bryozoa, but a much larger number of plants. Tbegeo benthos is pretty sharply divided 

 into ragranl geo-benthos, or animals, and sedentary geo-benthos, or plants, excepting some 



ol til.- lowest of the latter. 



