7& 



NATURE 



[December 2, 1922 



also one anemone as the central figure sitting on the 

 top of the shell — containing the hermit-crab — with its 

 column extending high above the shell and crab. 



When these hermit-crabs with their associated 

 anemones are caught fresh in the trawl it may be 

 observed that although the anemones come up closed 

 in no case are they sitting on the shell as is shown 

 in the well-known figures ; on the contrary, whether 

 there is onlv one or as many as three anemones 

 on a shell they are all found to be either hanging 

 from the shell with the disc region towards the 

 ground or are straining their bodies to reach their 

 discs over the side of the shell towards the ground 

 (see Fig. i). In order to obtain more informa- 

 tion, a collection of fresh hermit-crabs and ane- 

 mones was obtained by trawling in September 1920 

 and a few experiments made in a tank. The 

 hermit-crabs and anemones were isolated and kept 

 without food for a few da}'s, in the course of which 

 most of the anemones closed. At 11.30 a.m., 

 September 22, the crabs, carrying altogether 18 

 anemones, were fed with cockles and queens. At 

 12.5 p.m. all anemones were open with their discs 

 and tentacles spread flat out on the bottom of the 



Fig. 1. — Drawing from life of the Hermit-crab (Eupagurus bemhartlus) in 

 whelk with two anemones (< alliactis parasitica) shown in the natural fei 

 the commensal worm [Nereis fucala) in the act of taking food out of the 

 (About half the natural size.) 



tank (as is shown in Fig. 1) and being trailed about in 

 this position by the crabs. At 10 a.m., before the feed- 

 ing, two anemones were closed, three already had their 

 discs on the ground, and thirteen were held horizontally 

 from the apical region of the shell-house of the crab, 

 and at 1 p.m., after feeding, many were again closed 

 or with their bodies held horizontally. On September 

 29 the experiment was repeated, but this time fresh 

 dredgings onlv were thrown into the tank. All the 

 anemones soon put their discs flat on the ground, 

 and those which were sitting horizontally bobbed 

 their discs down on the ground within a few minutes, 

 almost as though the order " heads down " had been 

 given and obeyed. It was not possible to see whether 

 the unusual movements of the crabs on the addition 

 of food, or the smell of the added food, caused the 

 anemones to react as they did. 



On adding the food to the tank it was also observed 

 that the worms (Nereis fucata) living in the shells 

 inhabited by the hermit-crabs also came out to feed. 

 The hungry worms came out cautiously some time 

 after the hermit-crabs had begun to feed, and in 

 one case a worm was observer! to crawl alongside 

 tlie body of the crab (see Fig. 1), over the acti 1 

 mouth appendages, and literati}' to take with impunity 

 a piece of food from between the jaws of the crab 

 and bolt it. There seems to be little doubt that 

 this action of the worm is consciously tolerated by 

 the hermit-crab, as it was observed that the crab 

 can apparently control the exit of the worm from 

 the shell. It was found, however, that strange 



NO. 2770, VOL. I io] 



worms taken from other hermit-crab shells are not 

 regarded in a kindly manner by either the anemone 

 or the crab : worms fed to anemones are eaten, and 

 worms straying in the neighbourhood of hermit- 

 crabs were mercilessly torn up and tasted but rejei ted 

 as food. The spectacle of a hermit-crab cleaning 

 itself after feeding is a revelation of the value of 

 spines and hairs and of the meticulous cleanliness 

 of these animals, and cannot fail to impress the 

 observer with the pleasure — and even mild intoxica- 

 tion — experienced by the hermit-crab from the 

 feed. 



It is clear that the anemone derives advantage 

 from the hermit-crab by getting dragged about with 

 its tentacles on the ground and being given op- 

 portunities for picking up pieces of food left or lost 

 by the hermit-crab and for capturing other animals as 

 food. The hermit-crabs were not seen to pass on 

 pieces of food definitely to the anemones, but there 

 would always be a good chance of an anemone getting 

 some food front the table of the hermit-crab, owing 

 to the habit of the latter of tearing the food apart. 



The crab itself probably derives some measure of 

 protection from attacks from fishes owing to the 

 unpleasantness of its associated 

 anemones as food, but it is well 

 known in this laboratory that the 

 common ballan wrasse (Labrus 

 bergylta (maculatus)) will watch its 

 opportunity to seize a large claw 

 of a hermit-crab and shake it — 

 like a dog worrying a rat — with the 

 common result of extracting the 

 whole hermit-crab out of the shell- 

 house without touching the 

 anemone. 



The function of the worm in the 

 shell can scarcely be guessed at, 

 but the curious and constant wave- 

 like motion of the whole body of 

 the worm — which can be seen by 

 making a window in the shell — 

 will certainly keep up a strong 

 current of water around parts of 

 the body of the hermit-crab, and may assist the 

 hermit-crab in this way in the aeration of its 

 body or in the removal of effete products. The 

 advantage to the worm of obtaining shelter and of 

 partaking of the hermit-crab's food is obvious. 



J. H. Orton. 

 Marine Biological Laboratory, Plymouth, 

 November 9. 



a shell of the common 

 ding position, and with 

 jaws of the hermit-crab. 



First Lessons in Practical Biology. 



After being encouraged by favourable criticism, 

 both from the Press and from private individuals 

 (not in all cases personal friends), I was somewhat 

 surprised at the acerbity of the attack, published in 

 - 1 1 it. November 4, upon my unpretentious book 

 " First Lessons in Practical Biology." Helpful 

 criticism is welcome to an author, and the correction 

 of errors can be the making of a second edition of 

 a text-book ; but adverse criticism in which personal 

 bias of opinion is allowed to outweigh generally 

 accepted beliefs can have little value either for the 

 author or for the reading public. 



If " the telson is not a segment " I am consoled 

 bv the thought that two such standard works as 

 " Practical Zoology " (Marshall and Hurst) and 

 " Biology " (Parker) contain the same heresy. If 



the biramous appendage is not the primitive form 

 of crustacean appendage " I have still to read a more 

 convincing argument than that given in the " Cam- 

 bridge Natural History (Crustacea)." 



