138 Prof. Mcintosh on the 



Diphyes, besides other rare forms, make up a characteristic 

 pelagic fauna. 



In connexion with the consideration of the vast number of 

 free oceanic animals near our own shores, a feature, perhaps 

 not sufficiently appreciated, is the fact that a constant inter- 

 change takes place between the upper regions and the bottom, 

 and this at very considerable depths *. So far, indeed, as 

 present observations go, there is no reason why any region 

 of the water, say between 200 fathoms or more and the sur- 

 face, should be azoic f- Thus many of the deep-sea starfishes 

 have larvte which swim near the surface of the water, and 

 they again descend when they have reached a stage in which 

 the main features of the adults have been reproduced. Many 

 of the Pleuronectidfe, such as the plaice, turbot, and craig- 

 fluke, which habitually live on the bottom, produce eggs 

 which are truly pelagic and float near the surface of the water, 

 as also do the early embryos. The young, however, as they 

 grow older sink deeper and deeper in the water, until at a 

 certain stage they take up their residence at the bottom, like 

 their parents. Such animals, therefore, at different periods of 

 their existence inhabit separate zones of the water, and thus 

 form one of the great groups into which pelagic animals may 

 be divided, viz. those Temporarily Pelagic^ the other division 

 being constituted by those Permanently Pelagic. 



The area from which this temporary pelagic life is derived 

 is extensive, for every patch of sponge covering rocks, stones, 

 and seaweeds, many hydroid zoophytes and other coelen- 

 terates, many echinoderms, the majority of the annelids, 

 many Polyzoa and tunicates, and numerous shell-fishes, send 

 off periodically a succession of ciliated free-swimming larvje. 

 Moreover, such occurs not only between tide-marks but 

 wherever marine animals exist on the sea-bottom. 



In briefly alluding to the various forms which people the 

 region under consideration, on the east coast, it is found that 

 besides the pelagic fauna there is a pelagic flora, the most 

 abundant forms being diatoms and desmids,the former occurring 

 everyAvhere near the surface of the water, in the stomachs of 

 pelagic animals in mid-water, and in the alimentary cavities 

 of ascidians fixed to the bottom. The pelagic Foraminifera 

 and radiolarians again are equally abundant at the surface 

 and at the bottom, and the living as well as the dead may 

 pass from the upper to the lower region of the water. The 

 upper parts of the sea teem with Infusoria, such as Ceratium^ 



* Vide Report of H.M. Trawling Commissioners, 1884-5, p. 372 &c. 

 t Prof. Moseley is unable to give a decided opinion on this point, or 

 thinks that a vast region may be azoic. 



