58 



THE AUSTRALIAN MUSEUM MAGAZINE. 



Columbus had other and more satisfac- 

 tory reasons for his own confidence. 

 On account of its oceanic life, one 

 might suppose this little creature to be 

 one of the swimming crabs, which have 

 specially adapted jjaddle-shaped limbs. 

 This is not so; but the Sargasso Crab is 



Gall on a coral colony; this is caused 

 by the Irritation set up by the female marsu- 

 pial crab, which becomes enclosed in the gall. 

 Drawing — A. K. McCulloch. 



nevertheless enabled to move freely 

 through the water from one object to 

 another by means of closely-packed; 

 rows of fine hairs or eiliae arranged 

 along each border of the limbs. Another 

 adaptation is seen in the structure of 

 the terminal joint of each walking leg. 

 This is triangular in shape, and ii^ 

 armed with hooked sjiines, giving the 

 crab a foothold from wliicli it is not 

 easily dislodged. 



MARSUPIAL CRAB. 



One of the most curious adaptations 

 and one of the strangest places of abode 

 is seen in the case of the Marsupial 

 Crab ( Hapalocarcin m.s- m a /-.s upialis ) , 



which derives its name from the likeness 

 its abdomen bears to a pouch. This 

 Highly sjiecialised crustacean occurs oi: 

 the reefs off many parts of the tropical 

 Queensland coast, associating itself 

 witli delicate-limbed corals. Its pre- 

 sence on the coral colonies is indicated 

 1)V the occurrence of basket-like l)ulbous 



growths intermingled with the branches, 

 inside of each of which may be found 

 imj^risoned a female crab. The males, 

 on the other hand, are comparatively 

 minute, but are active and free-living. 

 They may often be seen clinging to the 

 branches of the coral if this latter is 

 withdrawn quickly from the water. In 

 their younger stages the female Mar- 

 supial Crabs, like the males, are free- 

 living; but they soon settle down upon 

 some coral colony, and so irritate the 

 living polyps that they grow abnor- 

 mally, and produce the extraordinary 

 structure which thenceforward forms 

 the home of the crab. Its formation is 

 largely controlled by means of certain 

 complicated water currents set up by 

 the breathing of the cral). By this 

 means a safe retreat is provided for 

 the crustacean, though the gall also be- 

 comes its prison, for the coral grows 

 completely round it and leaves only 

 small openings through which the water 

 currents pass. These carry both food 

 and oxygen to the imprisoned crab, 

 which remains for the rest of its life 

 within the gall. The males, however, 

 on account of their small size, are en- 

 abled to gain access to the females by 

 passing in and out of the openings . of 

 the galls. The young likewise escape 

 through the same apertures. 



SHELL-CASTING IX CRUSTACEANS. 



Many peoj^le know that a crustacean 

 casts its shell, but few are aware of the 

 process by which tliis is accomplished. 

 Furtlier, it will be news to those who 

 have not thought on the subject, that 

 this so-called shell represents the ani- 

 mal's skeleton, which, unlike the skele- 

 tons of most other animals of our ac- 

 (|uaintanee, is mainly external, and en- 

 closes the soft body of the crui'taeean. 

 This skeleton is composed of a hard 

 substance calle.l chitin, which resembles 

 horn, and is dejiosited in the outer 

 layer of the skin, wheve it forms a 

 firm armour to protect the body, eyes, 

 antennae and legs. With a little ima- 

 gination, we can liken this covering to 

 the jointed armour worn by tlie knights 

 of olden times, consisting as it does of 

 a number of plates moulded to the form 

 of tlie wearer's body, and united with 

 one another bv flexil)le joints. But if 



