CRABS AND LOBSTERS 573 



during development and growth is tremendous. It is estimated, for instance, 

 that only one out of every 38,000, or "003 per cent., attains maturity, this being 

 about one for every berried female. In the case of crabs the mortality is even 

 greater, the estimate being that one adult survives out of every 900,000 fry, or 

 about one for each female with eggs. 



Crabs are most numerously represented in tropical seas, where they attain 

 their maximum development both in size and in brilliance of colouring. The 

 largest member of the whole class is the great spider-crab (Macrochira kcempferi) 

 of Japan, in which the shell measures fifteen inches in length, while the longest pair 

 of limbs of the male may reach, when extended, to a span of more than ten feet. 

 The largest shell is, however, that of the Australian giant-crab (Pseudocarcinus 

 gigas), which may measure as much as two feet in width. Another large and 

 striking Indo- Pacific species, belonging to the long-tailed group, is Scylla serrata, 

 which on the coast of Natal lives in deep holes, where it sits at the entrance to feed 

 as the tide comes in, while at the ebb it basks in the sun, when it falls an easy 

 prey to the spears of the Kafirs. Smaller, but quite as brilliantly coloured, is 

 Charybdis cruciata, in which the yellow shell bears in the centre a white cross 

 on a scarlet patch. Among other conspicuous forms, mention may be made of the 

 widely distributed Podophthalmus vigil, in which the large eyes are mounted on 

 unusually long stalks, while the shell is expanded into the shape of a spatula ; and 

 the New Zealand crayfish (Palinurus tumidus), which is a couple of feet in length, 

 and more than seven inches in diameter. The European lobster (Astacus, or 

 Romarus, vulgaris) may attain a weight of eleven or twelve pounds. 



Certain other kinds of animals, such as barnacles and sea-anemones, are in the 

 habit of affixing themselves to the shells of crabs and other crustaceans in order 

 to be carried about and thus obtain a larger supply of food than would otherwise 

 be the case. One of the most singular instances of this symbiosis, as it is called, 

 occurs in a crab originally described from Mauritius under the name of Melia 

 tesselata. When first described its habit of holding sea-anemones in its two front 

 claws was not noticed, but this was observed later both in Mauritius and in Ceylon. 

 The crab holds in each claw a small white sea-anemone, which it presents, with 

 the tentacles fully expanded, to every intruder, in 'true boxing attitude.' The 

 ground-colour of the crab is whitish with a rosy flush on the front of the shell, 

 which has also a pattern of black lines. Probably both the crab and the anemones 

 benefit by the association, the latter enjoying increased mobility, while the former 

 shelters and defends itself with the living gloves with which it is provided. The 

 stinging threads of the anemone are probably the active means of defence and offence. 



Hermit-crabs (Pagurus), it need scarcely be mentioned, protect their soft 

 bodies by becoming tenants of the empty shells of whelks and other gastropods 

 which they carry about as if part of themselves. In New Zealand a hermit-crab 

 (Ewpagwus stewarti) has been found in some cases inhabiting a massive polyzoon 

 apparently too big for the crab to move ; in other cases it sheltered in straight 

 tubes in a Millepora, these tubes perhaps having been originally formed round sea- 

 weeds, which subsequently rotted. 



Barnacles, which few persons unacquainted with natural history 



Es rn3.cl.63 



can be persuaded to believe are relatives of shrimps and lobsters, are 



