506 PROF. J. E. DUERDEN ON CRABS | Dec. 12, 
a result of stimulation by the meat juices emanating from the 
food on the disc. Fragments of meat or meat extract diffused 
around the anterior part of the crab called forth vigorous move- 
ments of the mouth-appendages and first pair of walking-legs, 
though directed towards no very definite end; but when the 
extract was applied towards one side or the other, there was a 
decided movement of the appendages in that direction. Similarly, 
juices emanating from the food on the polypal disc may be 
assumed to serve as the stimuli by which the reflexes are brought 
about, the source of the stimulation and direction of response 
being determined from the direction in which the juices reach 
the crab. 
When non-nutritive particles, such as fragments of shell or 
grains of sand, were placed upon the polypal disc they produced 
no movements on the part of the actinian; likewise there was no 
response from the crustacean. Also in other cases substances 
which called forth no responses on the part of the actinian failed 
to bring about reactions from the crab. A small spider fallen 
into the water, and thereby drowned, was given the actinian. 
The tentacles closed over it momentarily, then withdrew, leaving 
the spider exposed on the disc. In this case the crab made no 
attempt to abstract the spider from the polyp, and after a time it 
was rejected by the latter. Fragments of bread and small pieces 
of paper placed on the polypal disc called forth no response from 
the actinian nor any from the crab. In fact, throughout the 
observations the actinians and crabs responded or remained in- 
different to the same substances; in each case ingestion reflexes 
took place only towards nutritive substances from which stimula- 
tive juices might be supposed to emanate, while there was 
indifference or rejection towards what might be supposed to be 
non-nutritive substances. Where the food supplied was so small 
in bulk that the polyp ingested it without any attempt at ab- 
straction on the part of the crab, we may assume that the nutritive 
juices were so weak that they failed to reach the sensory organs 
of the crab, and thereby failed to stimulate it to activity. 
PoLYDECTUS. 
While searching among the blocks of coral rock for further 
examples of Melia, a single specimen of Polydectus cupilifera 
(Latr.) was secured, also bearing an actinian in each claw. Both 
in its form and behaviour the new crab presented a great contrast 
with Melia. The former is very hairy, sluggish, and irresponsive, 
while the latter is active and most readily responds to stimuli of 
all kinds. 
The actinians held by Polydectus were small specimens of a 
species of Phellia, which occurs in abundance on the under surface 
of rocks and stones all round the Hawaiian Islands. Externally 
the polyps are characterised by having a thick cuticle over the 
greater part of the column, a circular area at the apex (the 
