PARASITISM, ETC., ON THE SEA-SHORE 137 



for instance, states that the contact of the hermit crab 

 Pagunis arrosor with the anemone Adamsia rondeletii stimu- 

 lates the latter in perfectly definite ways. Similarly, the 

 occurrence of the anemone Antholoha reticulata upon the 

 back of a crab (not a hermit crab) is due to the fact that 

 the anemone directs its efforts towards the attainment of that 

 position. If the anemone is dislodged it attaches itself to 

 the sea-bottom, spreads its tentacles and waits. In four or 

 five days it frees itself and turns upside down. As soon as 

 the base of the animal comes in contact with the leg of a 

 crab it lays hold and folds itself about the limb. From this 

 position the anemone gradually climbs up on to the back of 

 the crab, and there estabUshes itself. On the part of an 

 animal without nerve ganglia this is an interesting piece of 

 deliberate behaviour. 



Among the most curious cases of commensalism are those 

 illustrated by certain species of crab which carry about 

 anemones in their claws. The crab Melia tessellata carries 

 either a Sagartia or a Bunodeopsis in each claw (Fig. 11). 

 These two anemones are interchangeable, and the crabs may 

 reject a small polyp of the one kind to take up a larger 

 specimen of the other. The anemones are dislodged by the 

 insertion of the crab's first walking leg between the animal 

 and the substratum. The crab then travels with the Actinians 

 expanded and directed forwards, sometimes waving them 

 from side to side. When irritated it will move the claws 

 towards the source of trouble, thereby placing the anemone 

 in what may be regarded as the most favourable defensive 

 or aggressive attitude. Food secured by the anemones is 

 abstracted by the crab, which uses for this purpose the first 

 pair of walking legs. The chelipeds have no other function 

 (whether for aggression, defence, or grasping) than that of 

 carrying the Actinians, and this habit seems to have become 

 essential to the crab though not to the anemone. The crab 

 secures most of its food from the anemone, and also protec- 

 tion through its stinging-cells. It is considered to be an 

 advantage to the anemone to be carried about, and so 

 brought into contact with prey, despite the disadvantage of 



