1026 PRINCIPLES OF STRATIGRAPHY 



though a few species were found by the Challenger at depths ex- 

 ceeding" 2,000 fathoms. Some species are cosmopoHtan and the 

 order is represented in nearly all waters, their shells occurring in 

 nearly all the bottom deposits. The animals are also abundant on 

 algas, over which they crawl slowly. The fresh-water Cypris 

 swims about, subject, however, to the influences by which other 

 members of the plankton are affected ; or it crawls about on the 

 vegetation. Cypris is also represented in brackish and salt water. 

 Its eggs have the power to withstand desiccation for a long time, 

 and hence the species can continue in water bodies which become 

 periodically dried up. as in desert regions. The larva of the ostra- 

 cods is a pelagic nauplius. 



Cirripcdia. The cirripeds, or barnacles, are marine sedentary 

 benthonic Crustacea which have degenerated much from the true 

 type of crustacean, owing, no doubt, to their attached mode of life. 

 The body is covered with calcareous plates variously arranged, 

 which fall apart after the death of the animal; after which, from 

 single pieces, it is quite impossible to determine the species, owing 

 to the great variation of the skeletal parts. (Darwin.) Balanus 

 and its congeners are sessile, being attached to the rocks and other 

 solid supports along the shore, seldom venturing into water of 

 great depth. Some species are periodically exposed for many 

 hours at low tide, some, in fact, never being covered more than one 

 or two hours at flood tide, so high up on the shore do they attach 

 themselves. Balanus has been found at a depth of 500 fathoms, 

 but it usually lives in lesser depths. Balanus iuiprovisus occurs also 

 in brackish water, and some species of this barnacle have been re- 

 ported from fresh water (Tscherniansky). Coronula diadema 

 leads an epi-nektonic life, attaching itself to the body of whales. 

 Verruca inccrta, a common West Indian type, occurs in the Glo- 

 bigerina ooze. Lepas and its congeners are pedunculate, attach- 

 ing themselves by a fleshy peduncle, which represents the elongated 

 Tiead end. The majority of the Lepadidje are pelagic, leading an 

 epi-planktonic existence, attached to floating logs, pumice, or other 

 objects. Three species of Lepas were found by the Challenger 

 attached to the Sargassum. Some members of this family descend 

 into deep water, Scalp elhim regiuni having been dredged by the 

 Challenger from nearly 3,000 fathoms. These abyssal cirripeds are 

 'usually attached to nodules, dead or living shells, corals, large 

 Crustacea, to spines of sea urchins and other objects. (Agassiz- 

 I, ii :50.) The cirripeds, upon hatching from the egg, pass through 

 several larval stages, the first of which is the nauplius stage. In 

 this the body is unsegmented, with median frontal eyes, dorsal 



