THE DECAPODA 297 



yet free from the carapace, and that the third thoracic limbs, like 

 the four following pairs, only appear as bilobed rudiments. The 

 uropods are present as rudiments, but the pleopods are not yet 

 indicated. A Schizopod-stage (Fig. 174, A) follows, with movable 

 paired eyes, with seven pairs of biramous thoracic appendages 

 functioning as swimming -feet, and with well -developed tail-fan. 

 Later stages (Fig. 174, B) show rudiments of the first five pleopods. 

 A Mastigopiis-st&ge (Fig. 174, C) intervenes before the assumption 

 of the adult form. 



The larvae of Sergestes, though differing remarkably in appear- 

 ance from those of Leucifer, conform closely to the same type of 

 development. The youngest known larvae are Protozoeae (Fig. 

 175, A), which differ from those of Leucifer in their compact 

 form and in the possession of stalked eyes and of biramous third 

 maxillipeds. The most characteristic feature, however, is the 

 armature of the carapace. A rostrum, a median dorsal, and a pair 

 of lateral spines are present as in Leucifer, but much stronger, 

 and each bearing a double row of secondary spines. The Zoea 

 (Elaphocaiis of Dana) has this spine armature still more developed, 

 and an additional pair of compound spines appear on either side 

 of the rostrum. In the Schizopod-stage (known as AcantJiosoma) 

 (Fig. 175, B) the armature of the carapace is very much reduced. 

 Before the adult stage is reached a Mastigopus- stage intervenes, 

 characterised by the temporary disappearance of the last two 

 pairs of thoracic limbs, which are present alike in the Acanthosoma 

 and in the adult animal. It is interesting to notice that in this 

 character Leucifer represents a permanent Mastigopus-iorm. 



In the remaining groups of Decapoda no case is known where 

 the larva is hatched at a stage preceding the Zoea, though in some 

 instances a larval cuticle, moulted soon after hatching, has been 

 supposed to present characters of the Protozoea. 



Among the Caridea the earliest larval form is a Zoea in which 

 the third thoracic appendages are already well developed. The 

 posterior thoracic region is undeveloped, though the abdominal 

 somites, with the exception of the last, are defined. The carapace 

 has a rostrum and supra-orbital and antennal spines, but no further 

 armature. In many cases the stage at hatching is still farther 

 advanced, the paired eyes are stalked and movable, and one or more 

 pairs of the posterior thoracic appendages are present as rudiments. 

 In spite of the retarded development of the last five thoracic somites, 

 it is noteworthy that the appendages appear in regular order from 

 before backwards, with the exception of the uropods, which generally 

 develop precociously. In the Schizopod-stage it is a very general 

 but not universal character of the Caridean larva that it is with- 

 out exopodites on the last thoracic feet. In many Caridea there 

 is still further abbreviation, leading to complete suppression of the 



