IOO Invertebrata. 



by the third pair of limbs, or the large antennae, con- 

 sisting of five basal joints succeeded by a long feeler. 

 The bases of the fourth pair of limbs are modified into 

 biting-jaws or mandibles, and they bear an internal 

 appendage named the mandibular palp. The fifth 

 and sixth pairs of limbs are also jaws, and are called 

 maxillae ; they also bear rudimental appendages. The 

 three segments that follow the head segments, and 

 are united thereto, make up the thorax, and their 

 limbs are also in the lobster modified into organs of 

 mastication, and hence are known by the name of 

 foot-jaws; each of these except the first bears outer 

 and inner appendages, but the third pair is of very 

 little use as a chewing organ, but bears a gill as does 

 also its anterior neighbour, the second pair of foot jaws. 

 Following the limbs of the cephalo-thorax, for so 

 the united head and thorax is often called, we come 

 to five pairs of walking legs, each pair being the limbs 

 borne by a segment of the abdomen. These five 

 abdominal segments are also in the lobster covered 

 over dorsally by the dorsal shell, but on the under 

 or ventral surface, their separateness can be very well 

 recognised. The first pair of limbs consist of the 

 pincers or chela. These formidable organs in the 

 lobster are made up of seven joints, the last but one 

 of these is very large, and its outer angle is prolonged 

 into a finger-like process capable of being opposed 

 to the last joint, thus making a grasping organ of 

 great power. In the lobster the two pincers are not 

 quite symmetrical ; one is armed along the edges of 

 the blades of the pincers with rough tubercles, the 

 other with small serratures ; the former claw is prob- 



