Biology of Pachygrapsus crassipes —Hi ATT 
187 
to their refuges, whereas small individuals seem 
content to defend only the crevice itself. 
On several occasions a crab was found in the 
same refuge for 2 successive days, indicating 
that some degree of stability is attained. The 
smaller crabs tend to remain in restricted areas 
and show more evidences of territoriality than 
do the larger crabs. However, the underlying 
factor here may not be innate territorialism but 
rather self-preservation, inasmuch as the crev¬ 
ices accepted by young crabs are sufficiently 
small to exclude the larger individuals which 
wander about the pool. The data secured seem 
to show that the virility order together with 
the number of desirable refuges in a tide pool 
combine to regulate the distribution of the 
animals. 
The gregariousness of grapsoid crabs lower 
on the strand (H. nudus and H. oregonensis) in 
contrast to the individualism of P. crassipes, 
together with the independent existence of fos- 
sorial land crabs, may indicate that territorialism 
is progressively more highly developed as crabs 
become adapted to a terrestrial existence. It is 
likely that this trend toward territoriality is 
associated with the comparatively spacious 
Lehensraum extending landward from the 
strand, in contrast to the narrow stratified zones 
so characteristic of the littoral area. 
Although these crabs live together in large 
numbers they neither exhibit co-operation with 
one another, nor manifest any tendency toward 
such communal existence as that displayed by 
many terrestrial arthropods. The writer has 
found no evidence that these animals associate 
for mutual aid either in foraging for food or 
for defensive purposes. Crabs appear to have 
their own refuges and are responsible for their 
own interests. In this respect they agree with 
other crustaceans, for although they possess an 
endless variety of structural adaptation suited 
to a multitude of habitats and modes of life, 
very few have taken advantage of the oppor¬ 
tunities offered by a communal association 
among members of the same species. 
DEFENSIVE MUTILATION AND REGENERATION 
Defensive Mutilation 
The ease with which P. crassipes severs its 
pereiopods, together with the high frequency 
of collected specimens found with regenerating 
appendages, makes it imperative that an investi¬ 
gation of these phenomena be made to evaluate 
their relationship to the general welfare of the 
animals. It is generally accepted by investigators 
of defensive mutilation that the automatic sev¬ 
erance of an appendage from the body is a 
reflex act. However, not until recently (Wood 
and Wood, 1932) was the mechanism whereby 
this is accomplished fully determined, although 
it had been frequently discussed for more than 
a century. To comprehend the interpretations 
presented in the literature and the observations 
made on P. crassipes, it is necessary to clarify 
the definitions of the terms which have been 
applied to self-mutilation and closely allied 
phenomena. Since the term autotomie was intro¬ 
duced by Fredericq (1883), investigators have 
included under it the following closely asso¬ 
ciated but distinct phenomena: 
Autopasy results when an outside agent 
is responsible for the severance of an ap¬ 
pendage at a pre-formed breakage plane 
(Pieron, 1907). 
Autotilly is the separation of an appendage 
at a pre-formed breakage plane with the 
assistance of mouth parts, chelae, or other 
pereiopods of the animal itself (Wood 
and Wood, 1932). 
Autotomy refers to the reflex severance of 
an appendage without aid from any source 
other than from the appendage severed 
(Fredericq, 1883). 
Autophagy is the act of consuming a part 
of the body, usually after severance from 
the remainder of the animal (Wood and 
Wood, op. cit.). 
The failure of early investigators in this 
field to distinguish between the foregoing types 
of self-mutilation has resulted in the publica- 
