208 
PACIFIC SCIENCE, Vol. II, July, 1948 
inant food supply; consequently this species 
adheres to the food type characterestically util¬ 
ized by terrestrial species. 
The reduction of gill volume relative to body 
volume, the ability to withstand desiccation, the 
eurythermal tolerance, the high locomotor de¬ 
velopment, the osmo-regulatory development, 
and the herbivorous food habits, all combine 
to substantiate the thesis that this species has 
progressed from a purely marine habitat toward 
a terrestrial existence. With these data at hand, 
it is possible to discuss with considerable assur¬ 
ance the route by which this species may be 
attaining a terrestrial life. Two routes to land 
are open: one via brackish to fresh water 
through estuaries and bays, and the other via 
the littoral area without first encountering de¬ 
creased salinity. Inasmuch as hypoosmotic regu¬ 
lation is more highly developed than hyperos¬ 
motic regulation, it is certain that the adapta¬ 
tion to land has progressed through the littoral 
area rather than via the estuarine route, notwith¬ 
standing the occurrence of P. crassipes in the 
more saline areas of bays and estuaries. In con¬ 
trast, the absence of hypoosmotic regulation, in 
conjunction with the highly developed hyperos¬ 
motic regulation, indicates that H. nudus and 
H. oregonensis are progressing toward a terres¬ 
trial existence via the estuarine route. 
Barrell (1916) and Lull (1917) minimize 
the number of animals which have attained land 
directly through the intertidal zone; but, if we 
may judge from the multitude of species now 
partially adjusted to land, there must have been 
many in the past. Inasmuch as this species is 
attaining or has achieved morphological, physi¬ 
ological, and behavioristic adaptations which 
enable it to withstand the drier conditions at¬ 
tendant to a near-terrestrial habitat, and inas¬ 
much as these adaptations coincide with those 
found in true land crabs, it is evident that 
this species, at the present time, has progressed 
toward a terrestrial existence via the littoral 
route. 
Barrell (op. cit .) also maintains that the 
rarity of passage of crustaceans, gastropods, and 
vertebrates from a truly marine to a truly terres¬ 
trial mode of life through the apparently open 
path of the tidal zone, contributes evidence that 
an unused food supply could not alone operate 
as a cause sufficient to induce this change. How¬ 
ever, the supposition that one or another factor 
is the primary cause for migration from sea 
to land is a somewhat limited point of view. 
The preservation of species depends upon the 
procurance of food, protection from enemies, 
reproduction, and continuous adjustment to 
continually changing environment; hence one 
lure is not sufficient cause for a migration of 
this magnitude. The utilization of algal types 
which occur high on the strand was only pos¬ 
sible after the crab was adapted to it, so that 
their utilization did not interfere with other 
exigencies of life. P. crassipes has, then, made 
progress toward the attainment of a terrestrial 
habitat, the main prerequisites being aerial 
respiration, water conservation, swiftness, and 
internal stability. 
SUMMARY 
1. The present investigation of Pachygrap>sus 
crassipes Randall, the lined shore crab, is con¬ 
cerned especially with its geographical and eco¬ 
logical distribution, intermolt cycle, molting, 
general habits and behavior, defensive mutila¬ 
tion and regeneration, predaceous and parasitic 
enemies, reproduction, and growth. In addition, 
information is advanced pertaining to the level 
attained by this species in the transition from a 
purely marine toward a terrestrial habitat. 
2. The authenticated geographical range of 
this species follows well-defined isotherms and 
extends along the western coast of North Amer¬ 
ica from latitude 45° N. to latitude 24° N., 
and along the coast of Japan and Korea from 
latitude 37° N. to latitude 34° N. Probable 
avenues of dispersal to the Orient from America 
are discussed, and locality records outside the 
established range are considered. 
3. The general littoral habitat of P. crassipes 
includes three distinct biotopes. Each of these 
biotopes provides the fundamental ecological 
