190 
PACIFIC SCIENCE, Vol. II, July, 1948 
Autotomy is difficult to perform because of 
the maximal contraction which the autotomizer 
muscle must exert on the rim of the basis in 
order to elevate the limb sufficiently high, to¬ 
gether with the additional tension required to 
autotomize the appendage. Proof of the occur¬ 
rence of this method was secured when two 
captive crabs severed all of the legs with the 
exception of the chelae and the fifth pair. 
Pereiopods 2, 3, and 4 probably were autotil- 
lized, but the fifth pair is articulated in a manner 
which prohibits the chelae from contacting it. 
Three days after the last autotilly, the fifth pair 
of appendages of one crab was severed. Five 
days after the last autotilly in the second crab, 
one of the fifth pair was severed. The fore¬ 
going behavior suggests two significant points; 
namely, (1) that autotomy of the type illus¬ 
trated in Figure 15 must have occurred, and 
(2) that the long interval between autotilly 
and autotomy may possibly be attributed to 
the poor condition of the animals after the 
wholesale severance of most of their appendages. 
It is possible that the interval between autotilly 
and autotomy was a period of convalescence, 
during which the animals regained the vigor 
necessary to accomplish this type of mutilation. 
Several of the captive crabs severed pereiopods 
2, 3, and 4 from one side; but few severed the 
fifth pair if those anterior had been cast pre¬ 
viously. 
In the laboratory a unique behaviorism de¬ 
signed to contribute to autotomy was observed 
during ecdysis. A crab which was having con¬ 
siderable difficulty in withdrawing the ambu¬ 
latory appendages was observed to sever three 
limbs (right pereiopods 2, 3, and 4) by auto¬ 
tilly. The second pereiopod of the left side 
was likewise autotillized, but in an attempt to 
sever left pereiopods 3 and 4 (left pereiopod 
5 was successfully exsheathed) the animal ele¬ 
vated the right side of the body until it de¬ 
scribed an angle of approximately 75° with the 
substrate. All podomeres of the left pereiopods 
rested on the bottom of the aquarium. In this 
manner the crab, in its weakened condition, 
brought the processes x and Y (Fig. 15) to¬ 
gether and effected autotomy. 
Autopasy is especially prevalent in this species 
because of its scurrying behavior. Crabs will 
sever a grasped appendage in a fraction of a 
second. To test the number of successive auto- 
pasies which an individual crab will voluntarily 
undergo when held by the tip of an ambulatory 
leg, 20 individuals were collected at random. 
Each animal was placed on the substrate in its 
normal habitat and a dactyl was held. The first 
ambulatory leg grasped was severed almost 
immediately by each of the individuals. An 
assistant rapidly re-collected the crabs. At no 
time did the crabs offer to employ the chelae 
in defense. In the second test another leg was 
held which was likewise severed; however, more 
time elapsed before autopasy ensued; each animal 
required from 2 to 10 seconds to complete the 
process. The re-collected crabs were put to a 
third test. At this time 11 of the 20 specimens 
attempted to defend themselves by employing 
the chelae; when this defense was frustrated, 
16 of the 20 cast the third appendage. The 
time varied between 30 seconds and 2 minutes. 
After re-securing the animals a fourth leg was 
held. Without exception, each crab made vio¬ 
lent slashes with the chelae. Three crabs severed 
the fourth leg in 45 seconds, 2 Vi minutes, and 
3 minutes and 10 seconds, respectively. None 
of the remaining 17 animals would cast the 
fourth leg. All of them became placid and 
reluctant to move. 
The reluctance of the animal to sever its 
chelae was evident. Without exception, when 
a cheliped was grasped, the free chela was 
immediately used to defend the animal. Whether 
this behavior was associated with the ability 
of the animals to move the chelae in the lateral 
and forward area or to some instinctive behavior 
to protect these valuable appendages is not 
known. When the free cheliped was success¬ 
fully parried, autopasy occurred without excep¬ 
tion. The second cheliped was cast but once in 
20 tests. 
Some investigators contend that autotomy 
cannot occur while the crab is in a soft-shelled 
condition; however, in P. crassipes autotomy, 
