Biology of Pachygrapsus crassipes —HlATT 
173 
eyes contributing little or nothing to food 
procurement. Therefore the experiments out¬ 
lined below were devised to test more specifi¬ 
cally the relative utilization of the three senses 
in the normal habitat. 
Experiment 1: A fragment of abalone viscera was 
wrapped in several layers of cheesecloth to make it 
invisible to the crabs, yet to provide ample oppor¬ 
tunity for the diffusion of meat juices through the 
water. Care was taken to keep the outside of the 
parcel free from meat juice. The parcel was secured 
by a string and lowered into the pool with a long 
pole. A small crab, originally 8 inches from the 
parcel, moved to it in 30 seconds. It picked at the 
cloth for 25 seconds and returned to its refuge. Eight 
minutes later a second and larger crab visited the 
parcel. Shortly thereafter several other large crabs 
reached the vicinity of the parcel. Increased activity 
followed, climaxed by periodic boxing contests (see 
p. 180). One large crab approached the parcel, 
turned around, and backed up to it with the fifth 
pereiopods extended in a tactile-like manner. After 
a few seconds the crab walked away from the parcel 
and repeated the backing-up procedure. The parcel 
was pulled about the pool by the large crabs, which 
alternately fought their competitors and examined 
the bait for a period of 20 minutes before its removal 
from the pool. 
The foregoing experiment was repeated with a 
rock substituted for the meat and wrapped as before. 
A small crab reached the parcel in 5 seconds, gave it 
a cursory examination and soon departed. Another 
approached the parcel 70 seconds later, climbed upon 
it to examine the surface with the dactyls, but soon 
moved away. A third crab arrived shortly thereafter, 
pinched the parcel, and left it in 4 seconds. During 
the remaining 15-minute interval no other crabs 
came to the parcel. 
After the parcel containing the stone was removed, 
another parcel containing abalone viscera was intro¬ 
duced. It was significant to note that the first small 
crab reached the parcel after 1 minute had elapsed. 
This individual pinched the parcel a single time and 
immediately departed. Within the first 7 minutes 
three crabs reached the parcel but left after a hasty 
examination. Shortly thereafter, a large individual 
approached, backed up to the parcel, and meticulously 
examined it with the dactyls of the fifth pereiopods. 
Several more crabs approached, examined the parcel, 
and engaged in frequent contests; but they notably 
seized each lull in the fighting to examine the parcel 
further. Considerable milling about with frequent 
tugging at the parcel ensued for the remainder of the 
15-minute period. 
Experiment 2: A parcel containing abalone viscera, 
similar to that of the preceding experiment, was 
lowered upon the rocks bordering a tide pool. Al¬ 
though the parcel was within the usual range of many 
crabs, only two approached it; these abandoned it 
after a cursory examination. Other crabs walked close 
by, but none attempted to investigate the parcel in a 
15-minute period. 
The above procedure was repeated with a rock sub¬ 
stituted for the meat. The parcel was placed near 
several crabs on the rocks but all ignored it. After 
3 minutes a small crab approached it, and after 6 
minutes a larger individual reached the parcel; how¬ 
ever, both retreated after a hasty investigation. No 
other crabs ventured near the parcel in a 20-minute 
interval. 
Experiment 3: A pebble smeared with abalone 
intestinal chyme was tossed into a pool. In 45 seconds 
a small crab seized the pebble in one cheliped and 
picked at it with the other, frequently bringing the 
latter appendage to the mouth. Within 30 seconds 
several crabs emerged and milled about the baited 
region. Pugnacity was intense, but the foremost ac¬ 
tivity centered on a thorough examination of the 
substrate with the pereiopodal dactyls and the chelae. 
The procedure was repeated, with a clean pebble 
substituted for the smeared one. In 10 seconds a small 
crab located the pebble but abandoned it almost 
immediately. No further activity occurred near the 
second pebble for a 15-minute period. 
Experiment 4: An abalone fragment was tossed 
into a pool. The splash stimulated the crabs to seek 
refuge. None responded positively to the food for 
5 Vi minutes until a large crab emerged slowly from 
a near-by refuge and traveled in the general direction 
of the meat. The animal seemed to grope its way 
toward the meat in a manner which suggested the 
reception of chemical rather than visual stimuli. After 
this crab discovered the meat and removed it, several 
others congregated at the baited region and milled 
about it. The substrate was meticulously examined 
with the tips of the chelae which were frequently 
elevated and drawn to the mouth, thereby exhibiting 
evidence of strong stimulation by the juices in the 
water. 
The same procedure was repeated but the abalone 
meat was first immersed in CS 2 . After 30 seconds had 
elapsed, a crab seized the bait, conveyed it out of the 
pool to a position on the rock wall, and devoured 
it as readily as normal flesh. 
Experiment 5: A fragment of abalone was tossed 
onto the rocks within sight of four crabs. The meat 
was seized by one individual in 55 seconds. 
The same procedure was repeated with a piece of 
abalone previously immersed in CS 2 . It was tossed 
