ANNULOSA : CRUSTACEA. 



215 



meet along the back, and give way preparatory to the moult. 

 The tergal elements of the thoracic rings are not developed in 

 either Crabs or Lobsters ; when these rings are exposed by 

 lifting up the cephalothoracic shield, the epimeral parts alone 

 are seen, converging obliquely towards one another, but not 

 joined at their apices." (Owen.) 



Fig. 71. Macrura. Common Lobster (Homarus vulgaris). i. First pair of legs, 

 constituting the great chelae or nipping claws ; 2. Second pair of legs, also chelate ; 

 3. Third pair of legs, also chelate ; 4 and 5. Last two pairs of ambulatory legs, with 

 simply pointed extremities ; a. Antennules ; go. Great antennas ; ca. Carapace. 



The first segment of the head bears the compound eyes, 

 which are supported upon long and movable eye-stalks or 

 peduncles. Behind these come two pairs of jointed tactile 



