Ixxxii REPORT—1858. 
life is that which parallels the perpendicular distribution of plants. Edward 
Forbes, availing himself of the valuable results of a systematic use of the 
dredge, first showed that marine animals and plants varied according to the 
depth at which they lived, in a manner very analogous to the changes in the 
forms and species of vegetation observed in the ascent of a tropical moun- 
tain. He has expressed these facts by defining five bathymetrical zones, or 
belts of depth, which he calls,—1, Littoral; 2, Circumlittoral; 3, Median; 
4, Infra-median ; 5, Abyssal. 
The life-forms of these zones vary, of course, according to the nature of 
the sea-bottom; and are modified by those primitive or creative laws that 
have caused representative species in distant localities under like physical © 
conditions,—species related by analogy. 
Very much remains to be observed and studied by Naturalists in different 
parts of the globe, under the guidance of the generalizations thus sketched 
out, to the completion of a perfect theory. But in the progress to this, the 
results cannot fail to be practically most valuable. A shell or a sea-weed, 
whose relations to depth are thus understood, may afford important in- 
formation or warning to the navigator. To the geologist the distribution of 
marine life according to the zones of depth has given the clue to the deter- 
mination of the depth of the seas in which certain formations have been 
deposited. 
By the light of these laws of geographical distribution we view with quite 
a new interest the shells, corals, and sea-weeds of our own shores. We trace 
the regions whence they have been invaded by races not aboriginally be- 
longing to our seas; we obtain indications of irruptions of sea-currents of 
dates anterior to the present arrangements of land and water. Thus, part of 
our marine fauna has been traced back to the older pliocene period, part to 
the somewhat newer period of the red-crag, part to the still more recent 
glacial period—all these being anterior to the constitution of the ‘ Celtic 
Province,’ as it is now displayed. 
With regard to the class of Fishes, some families, the Sharks (Squaloids), 
Herrings (Halecoids), and Mackerel-kind (Scomberoids), are cosmopolitan. 
The Labyrinthodonts are limited to the Indian Ocean; the Goniodonts to 
the rivers of South America; the Lepidostei to those of North America ; the 
Polypieri to those of Africa. The fish called Chaca is restricted to the Lake 
Baikal, and the blind ‘ Amblyopsis’ to the Mammoth cave : just as the Pro- 
teus amongst amphibious reptiles is confined to the caverns of Carinthia. 
The class of animals to which the restrictive laws of geographical distri- 
bution might seem least applicable is that of Birds: their peculiar powers of 
locomotion, associated in numerous species with migratory habits, might seem 
to render them independent of every influence save those of climate and of 
food, which directly affect the conditions of their existence. Yet the 
long-winged Albatros is never met with north of the equator; nor does 
the Condor soar above other mountains than the Andes. The geogra- 
