METAZOA CRUSTACEA. 341 



Packed closely together under the abdomen are the 

 leaf-like respiratory organs, while the sixth or terminal 

 abdominal segment bears a pair of caudal appendages. 



MACROURA. 



Lucifer (PL 838) is one of the few Macrouran Crusta- 

 cea which pass through a nauplius stage (PL 838, fig. i). 

 It possesses at this time the three pairs of locomotor 

 appendages and an ocellus, but as yet there is no cara- 

 pace nor compound eyes. 



The nauplius develops into the zoe'a stage (fig. 2), 

 when the antennae and mandibles are still used for swim- 

 ming. The abdomen and its telson have developed and 

 the cephalothorax is provided with a carapace. 



In the next or Schizopod stage (fig. 3) the antennae 

 and mandibles have lost their locomotive function and 

 stalked eyes appear with the ocellus. 



When this Schizopod larva moults the Mastigopus or 

 young Lucifer stage (fig. 4) reveals a marked change in 

 the forward part of the cephalothorax. The segments 

 bearing the eye-stalks and two pairs of antennae are car- 

 ried far forward, while the hinder segments of the ceph- 

 alothorax bear the mouth parts and thoracic legs. The 

 adult does not differ essentially from PL 838, fig. 4. The 

 anterior segments extend farther forward ; the first pair 

 of thoracic legs are vestigial, while the remaining four 

 pairs are adapted for swimming, being abundantly sup- 

 plied with hairs. The abdominal appendages borne on 

 the six abdominal segments also aid the thoracic legs in 

 swimming. 



Penaeus, like Lucifer, leaves the egg in a nauplius 

 condition. The adult Penaeus canaliculatus Oliv. (No. 

 839) is larger than most shrimps and it has elaborated 

 some of the typical features of this group. The long 

 pointed rostrum of the carapace is notched on the upper 



