ARTHROPODA 



[CH. 



appearance. The body is of an 

 elongated pear shape, and consists 

 of a large round head and a 

 tapering trunk of comparatively 

 few segments. The carapace so 

 characteristic of the preceding 

 order is entirely absent. The head 

 bears a single median eye in front, 

 the lateral compound eyes so 

 conspicuous in most Crustacea 

 being absent. Attached to the head 

 are six pairs of appendages, two 

 pairs of antennae, a pair of man- 

 dibles, two pairs of maxillae and a 

 pair of short but jointed leg-like 

 appendages termed maxillipedes. 

 The head is not separated from the 

 trunk by any constriction. The 

 latter bears four pairs of swimming 

 feet of a typical forked pattern. 

 Each of these appendages is some- 

 thing like a \. The base of the 

 limb consists of one or two joints 

 constituting the protopodite. The 

 two forks are of course theexopodite 

 and endopodite. Both are flattened, 

 consisting of stout joints each of 

 which bears spines, and the whole 

 forms a convenient paddle. Each 

 limb is also jointed to its fellow of 

 the opposite side by a transverse 

 movable ridge so that the right 



cannot move without the left. 

 By ^ simultaneous action of all 



1. Antennule. 2. Antenna, the limbs of the trunk, the animal 



3. Mandible. 4. 1st maxilla. nr aKlorl fn PYPPH+P a <jpripi of 

 5. The two halves of the 2nd 1S enablecl to exec 

 maxillae sometimes called inner swift darts through the water; 



by the ^^ of the gecond ftn . 



tennae a slow, gliding movement 

 is carried out, whilst the max- 



plate connecting the right and illipedes by sweeping movements 

 left limb of each pair. 



and outer maxillipedes. 6-9. 1st- 

 4th thoracic* limbs. 10. Eye. 

 11. Bristles near male generative 

 opening. 12. Caudal fork. 



IB. Mouth. 14. Copula or 



