126 
PACIFIC SCIENCE, VoL XIII, April, 1959 
terrestrial than by aquatic species of the same 
family, and there is a longer growth and 
breeding period. Carrying of the female by the 
male for long periods is obviated and may be 
entirely lacking, and the time after egg laying 
during which fertilisation is possible has been 
lengthened, thereby increasing the chances 
of mating. This would greatly facilitate entry 
into the terrestrial environment, especially 
since it appears first in supralittoral species. 
5. There is a tendency for pleopods to be 
reduced to vestigial stumps, although species 
found high above sea level may have fully 
developed pleopods. Their absence in some 
species suggests that sufficient air is available 
to the respiratory surfaces without need of a 
pleopod-created current of air over the gills. 
In some species there is a marked develop- 
ment in size of gills. 
6. The terrestrial species show strong evi- 
dence of endemism. This is probably due 
partly to the nature of their environment and 
partly to lack of available transport as com- 
pared with marine and littoral species, al- 
though the advent of man has complicated 
distribution patterns to some degree. In at 
least two genera, Talitrus and Orchestia, ter- 
restrial species have arisen independently 
from littoral species. 
7. Moisture requirements are met by the 
leafrnould environment and behavioural pat- 
terns of the animals. 
8. There is some evidence that excretory 
problems have been solved, not by a change 
in end products of excretion, but by a general 
slowing down and suppression of nitrogen 
metabolism. 
9. The leafrnould environment provides 
conditions most favourable to colonisation 
by a marine or littoral group of animals and 
requires a minimum of physiological or 
morphological adaptations. 
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