196 DECAPOD CRUSTACEA. PART in. 



is another appendage, shorter and rather more com- 

 pressed. There are three pairs of claws, each composed 

 of three joints, and ending in four long slender hairs : 

 the claws stand at right angles to the body. The young, 

 when it escapes from the egg, is quite soft, but it rapidly 

 hardens by the deposition of calcareous matter on its 

 surface. The progress of the consolidation is shown by 

 the circulation of the white blood in the hollow dorsal 

 spine. When the creature is yet soft, the blood globules 

 may be seen ascending to its apex ; but, as the consolida- 

 tion advances, the circulation becomes more and more 

 limited till at length it is confined to the base. This 

 creature, whose shield is sap green and the rest trans- 

 parent, swims with great activity, beating the water 

 with his claws and tail. Such is the first stage in the 

 life of the common shore crab. At this period the 

 young of the Decapods bear a strong resemblance to one 

 another, whether they are afterwards to become long or 

 short tailed crustaceans. 



After a time this creature loses its activity, moults, 

 and is no longer to be recognised as the same, so great 

 is the change (fig. 148, B). The dorsal spine has vanished, 

 the shield has become flatter, its anterior part pointed, 

 the eyes raised on stalks, and certain rudimentary or- 

 gans that were below the eyes now form long antennae. 

 The first pair of feet have got hands, the others are 

 jointed and simple, except the last pair, which are still 

 natatory : with these and with the tail, which is now 

 much smaller, these creatures swim and congregate 

 round sea-weeds and floating objects. After the third 

 moult they have the form of a crab, though neither that 

 of the genus nor species of the parent (fig. 148, c). The 

 tail is folded under a square carapace, the four pairs of 

 walking feet spread widely and laterally, while the great 

 hand-feet attached to the anterior sides of the carapace 

 stretch straightforwards, the antennae are short, and the 



