Biology of Pachygrapsus crassipes —Hi ATT 
209 
requirements of this eurytopic species, viz., a 
hard substrate containing refuge places, gen¬ 
erally devoid of loose stones, sand, or mud, 
and possessing a more or less luxuriant growth 
of ulvaceous or filamentous algae. The inter¬ 
specific relationship between the three grapsoid 
crabs which range on the highest littoral hori¬ 
zon are described with respect to morphological, 
physiological, and behavioristic differences. 
4. A study of the seriation of morphological 
transformations during the intermolt cycle ad¬ 
vances this knowledge to the grapsoid group. 
External morphological characters are desig¬ 
nated as indicators of internal change. These 
characters should enable investigators to diag¬ 
nose accurately the stages within the intermolt 
cycle. A framework upon which to base accu¬ 
rate observations on both experimental and 
behavioristic data is thereby provided. The 
utility of such criteria to disclose periodicity 
within a single intermolt interval is conclusively 
confirmed by an examination of several hundred 
wild specimens. 
5. Exuviation is described in detail and its 
critical relationship to the life of the crab is 
made apparent. The incidence of molting is 
clearly demonstrated to be associated directly 
with the temperature of the water; the exuvial 
frequency is highest in summer months and 
relatively low from November to March. Post- 
exuvial expansion is nearly completed in 3 
hours. The individual size increment after ecdysis 
is highly variable, and the percentage of size 
increment varies inversely with the initial size 
and the age. Comparative studies on the post- 
exuvial size increments of male and female 
crabs indicate that no significant variation occurs 
until an initial width of approximately 25 milli¬ 
meters is attained. Thereafter, females exhibit 
a smaller post-exuvial size increment. Male 
crabs have been estimated to undergo 18 molts 
and females 21 molts before attaining maximum 
size, which is reached in a minimum of 3 years. 
6. Visual, chemical, and tactile perception 
are well developed in this species. Odor has 
no stimulatory effect. When submerged food 
is sought, visual perception generally precedes 
either chemical or tactile, but chemical percep¬ 
tion becomes predominant after a brief interval 
of time. Vision attains predominance during 
diurnal aerial activity; the tactile sense gains 
ascendancy after dusk. Although this species 
does not respond to sound vibrations within 
man’s range, the tactile sense is a significant 
factor in regulating the activities of this crab. 
7. This species is versatile with respect to 
directional locomotion, and is transitional be¬ 
tween purely aquatic and terrestrial brachyurans 
with respect to speed. 
8. P. crassipes may be designated essentially 
an herbivore, ordinarily a grazing herbivore, 
less commonly a plant scavenger, while facul¬ 
tatively a carnivore, chiefly an animal scavenger, 
and less often a predator. 
9. Field data show that periodic changes in 
daily temperature, tides, exposure, and illumina¬ 
tion have created a behavior pattern in these 
animals which seldom deviates from the stand¬ 
ard and which approaches a monotony of repeti¬ 
tions. 
10. The precocity and boldness of the young 
crabs of this species are probably attributable 
to their lack of experience and inhibitions, 
rather than to the relatively large, faceted eye- 
surface. The older and larger crabs with a 
greater faceted eye-surface indulge in the varied 
activities with more reserve and caution. 
11. Advanced territorial relationships do not 
exist for P. crassipes. Refuges are defended but 
no individual forage areas are protected. There 
is no tendency toward social aggregation. 
12. Defensive mutilation in this species 
occurs frequently and is easily achieved. The 
mechanism underlying this phenomenon is de¬ 
scribed in detail, and comparisons are made 
with other brachyuran species. 
13. Experimental results show that a point 
is reached during the final synthesis of the 
integument (intermolt stage C 4 ) before which 
regeneration of a complete appendage will 
ensue prior to ecdysis, and after which regenera¬ 
tion is inhibited prior to ecdysis. Three sue- 
