THE AUSTRALIAN MUSEUM MAGAZINE. 



5D 



a knight had been placed in arm^in' a. 

 a baby, he wuuid have hail to change 

 his suit many times before he became a 

 man. This applies equally to the case 

 of the crustacean; each suit of its ar- 

 mour is of a detinite size, and cannot 

 be increased. As it becomes too small 

 for the growing body of its occupant, 

 it must be cast off and replaced by a 

 new one, a i)rocedure which happens 

 many times throughout its life, when 

 it has to undergo a higidy complicated 

 process of moulting in order to with- 

 draw from its chitinous case. 



It will be convenient to accept tiie 

 moulting process of a prawn as typify- 

 ing the same happening among all the 

 other members of the Crustacean group. 

 The young prawn periodically experi- 

 ences a feeling of unrest and discom- 

 fort generally, owing to the tightening 

 of his armour upon his growing tissues. 

 He searches around for some secluded 

 spot where he will be safe from the 

 observation of his ever watchful enemies. 

 Having found one, he secures a tirm 

 hold with his feet, and sways his l)ody 

 to and fro, so as to loosen the armour 

 plating from the softer parts within. 

 This motion causes a slit to appear be- 

 tween the shield covering his back and 

 the plates of his abdomen. Through 

 this he gradually draws his head and 

 shoulders, bringing with them antennae 

 and eye-stalks, legs and feet, as perfect 

 as before, and having even their tiny 

 spines and hairs upon them; then witli 

 a sudden jerk he pulls out his abdomen 

 and leaves his clear transparent shell 

 so perfect that even the coverings of 

 tlie eyes, and the armoured lining of his 

 stomach and digestive tract remain, 

 and one might believe the real ]n-awn 

 stood upon the rock. The creature is 

 now so weak that he rolls helplessly 

 over, his soft body being so flaccid that 

 be is scarcely able to support himself 

 in position. At this stage he is so 

 helpless, that if any animal were to 

 seize upon him, he would be quite un- 

 able to defend himself. Knowing this, 

 he strikes out as soon as he can. and 

 feverishly works his swimmerets as they 

 gradually stiffen and strengthen, and 

 strives to swim or creep only in jilacc^ 

 of safety. There he stays until his 

 new enlarged coat of armour, which has 

 long been forming beneath the latelv 



discarded one, hardens sufficiently to 

 enable him to sally forth as a valiant 

 prawn again. Such is the procedure of 

 moulting or "ecdysis" in a prawn, 

 whici) differs only in detail from that 

 of the otlier members of tlie Crustacea. 



HERMIT CRABS. 



'1 he name Hermit Crab is ])()pularly 

 applied to those well known crabs 

 which have the strange hal)it of uti- 

 lising the empty shells of Shell-tish or 

 Molluscs for the protection of their 

 soft abdomens. This member has no 

 hard outer covering as in most other 

 crabs, but the whole is quite fleshy, 

 and would oft'er a tempting morsel to 

 other hungi-y sea animals if left ex- 

 posed to their gaze. The half-naked 

 crab therefore hides itself within the 

 cavity of a stolen shell, and it i.s so 

 modified that it twists naturally into 

 its spiral home. The anterior part of 

 the body is well protected by a hard 

 shelly arniiiur. One of tlie claws is 

 much l)igger tlian the other, and closes 

 the opening of the shell after the rest 

 of the body is drawn in, l)arring the 

 door against intruders. It is thus so 

 effectually protected that it is rarely in 

 danger, except when the era)) is chang- 

 ing from an old shell, which has be- 

 come too small for it, to a larger new- 

 one; tliis move is performed wM^nder- 

 fully (juickly, the crab never leaving 

 its old house till it has found a new- 

 one. Two formidable pai.^s of legs 

 follow the large claws, and their 

 strong, pointed, terminal joints are 

 able to secure a firm hold of the 

 ground when the crab is moving from 

 place to place and dragging his 

 weighty shell after him. The rest of 

 the appendages are modified to accom- 

 modate the crab's body in his spiral 

 shelly house. 



Somfe hermit crabs are terrestrial, 

 though they pass their earlier stages in 

 salt water. These ordinarily, like their 

 marine cousins, live in shells, but other 

 liollow objects, such as a })roken coco- 

 nut, or even a cracked test tul>e dis- 

 carded by a naturalist, have been 

 adopted. These land hermits are often 

 found great distances from the shore, 

 which accounts for the presence of 

 large marine sliells high up in the hills 

 of tropical islands. 



