382 



that such oozes, when found in a fossil state,* indicate deep 

 sea. The absence of chistic sediment may be due to the \ow 

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

 level, thus allowing Avater of moderate dejjth near shore to 

 be free from detrital nmterial. 



The term nekton, derived from theGreek vj/x", toswim, was 

 introduced bv Hteckel in 1800, t for those animals which lead 

 an actively swimming- life. The grou]) is typified by the class 

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

 head, and perfect bilateral synmietry, 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 ap|)endages for balancing and steering are 

 usually })resent. The body is non-transparent, and a cal- 

 careous sup[)orting skeleton is ordinaril}' develo])ed. 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 jiivOo<;, the depths of the sea, was 

 likewise introduced by Hteckel in 1S<)(). It covers those 

 organisms which inhabit the sea-bo ttoni.j; 



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 the 

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

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

 generally entondjed in the region where they have lived, 

 instead of being deposited anywhere, as is the case with 

 planktonic and nektonic organisms. The sedentary benthos 



*Styliolina limestone of the Genesee. 



tPlanktonstudien — TO V€ktov, that which swims. 



X Fish are typical halo nektonic and limno-nektonie animals. Greo-nektonic animals are 

 repre.sented by H.ving insects, reptiles, birds, and mammals. Xone of these lead a perma- 

 nently nekt(jnic life in the air, for all return more or less frequently to the substratum. 

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

 ered as nekton of the air, 



§ To speak of fluvial or limno-benthos, and 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 etymological 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. The geo-benthos is pretty s^iarply divided 

 into vagrant geo-benthos, or animals, and sedentary geo-benthos. or plants', excepting some 

 of the lowest of the latter. 



