64 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



stages of its growth, the abdominal segments are successively sepa- 

 rated from the telson and acquire pleopods. The five thoracic ap- 

 pendages lose their exopodites and take on the adult form, those of 

 the second segment becoming typical raptorial fangs in the fourth 

 instar. Later the appendages appear on the last three segments of 

 the thorax. In the second instar the eyes are stalked. 



The other first-larval form, termed a pseudozoea (fig. 24 B), occurs 

 in species of SquiUa, Gonodactylus, and probably of other genera. 

 The eyes in this form are stalked at hatching. The thorax is fully 

 segmented, but only the first two segments bear appendages, and those 

 of the second segment are raptorial fangs. The short carapace has 

 small spines on its anterior and posterior angles, and leaves four 

 posterior thoracic segments uncovered. The abdomen has five free 

 segments, of which the first four bear pleopods, but the sixth is still 

 united with the telson. 



Squilla mantis, according to Giesbrecht, goes through 10 larval 

 instars. The first two live on the bottom, but after the second instar 

 the larva becomes pelagic, swimming with the pleopods. In the sec- 

 ond propelagic instar (fig. 24 C) there is little change from the first 

 (B) except for an increase in size and a lengthening of the posterior 

 carapace spines, which in the first pelagic instar (D, E) become much 

 longer and widely divergent. In the third pelagic instar rudiments of 

 the third, fourth, and fifth thoracic appendages appear, and become 

 longer in the next stage, when also the appendages of segments six, 

 seven, and eight are developed. The sixth segment of the abdomen 

 becomes free from the telson in the seventh instar. The last pelagic 

 larva (F) has essentially the structure of the adult (G) except for the 

 large carapace, which now covers all but one of the thoracic segments. 

 After about the fifth instar, Giesbrecht says, the two larval forms, 

 originating with the antezoea and the pseudozoea, become struc- 

 turally alike. 



The principal structural changes during the life of the stomatopod 

 take place at the transformation of the larva (fig. 24 F) into the adult 

 (G). Even here, however, the only essential change affects the 

 carapace, which is much shortened and narrowed and loses its pos- 

 terior spines. Instead of covering most of the thorax as in the larva 

 (D, F) the carapace of the adult leaves the last four thoracic seg- 

 ments exposed. In this respect the carapace reverts to its relative 

 length in the first propelagic larva (B). It is evident, therefore, that 

 the larval development of the back shield is a metamorphic adaptation 

 to the pelagic life of the larva, probably to assist in keeping the larva 

 afloat. The relative length of the larval carapace varies in different 



