1905. ] BEARING ACTINIANS IN THEIR CLAWS. 503 
oral dise and tentacles turned upwards, this being the usual rela- 
tionship when first captured. 
Whenever an actinian was removed from the claw of a crab, 
certain cleansing-operations on the part of the latter invariably 
took place. Ordinarily the claws have particles of débris adhering 
to the hairs with which they are provided, as well as to the general 
surface of the skeleton, the amount being undoubtedly increased 
by the presence of mucus from the actinian. On the chelipeds 
becoming unoccupied they were turned towards the mouth, and 
the masticatory appendages, which are richly provided with bristles 
and spines, at once began a series of scraping or combing move- 
ments over them. So effective were these, that within a short 
time the claws were altogether cleansed of any adhering foreign 
particles and presented a much fresher appearance. 
REACTIONS. 
Under ordinary circumstances the crab when at rest holds its 
two chelipeds bent towards itself, and the actinians are inclined 
upwards and outwards with the tentacles fully expanded, thus 
masking to a certain extent the anterior part of the crab. When 
walking the chelipeds are held more forwards, and the actinians 
are then presented in what can be best described as a threatening 
attitude. It would be impossible for any animal of moderate 
size to molest the crab in front without touching the polyps. Some- 
times the claws are held downwards so that the polyps touch the 
bottom of the vessel, and on being dragged over it the mucus with 
which the body is covered leads to the adherence of debris. 
If any part of the crab be touched in front, the reflexes are such 
that the chelipeds are at once extended in the direction whence the 
stimulus proceeds, the polyps being thereby raised and presented 
in a defensive attitude. Likewise when irritated from the side, 
poth chele are turned laterally, the polyps again being directed 
towards the region whence the stimulus comes. Similarly, if 
touched on the upper surface of the carapace or posterior part of 
the body, the actinians are turned upwards and backwards: in 
fact, by varying the part stimulated, the chelipeds can be made 
to turn through about two-thirds of a circle ina vertical direction, 
and in addition they can perform complex lateral movements. In 
every case, it may be said that the responses of the crab are of 
such a nature that the claws bearing the actinians are turned 
towards the part irritated, thereby placing the polyps in a position 
most favourable for defence or offence. The reflexes are usually 
rapid and continue for some time, first in one direction and then 
in another, according to the region irritated. At the same time 
the crab generally moves away from the stimulus, backwards or 
forwards, though the claw reaction, the striking out, always occurs 
as a preliminary measure: retreat on molestation is by no means 
so readily resorted to as in most crabs. 
It is of much importance to find that exactly the same responses 
Proc. Zoou, Soc.—1905, Vou. II. No, XXXIV. 34 
