POST-I'UERULUS STAGE OF JASUS LALANDII. 



191 



The recognised characters which distinguish the larval puerulus from the 

 adult are (1) the large size of the pleopods, and particularly the presence of 

 special coupling hooks at the end ct the appendix interna, which join the 

 pleopods of opposite sides of the body together in pairs, (2) carapace and 

 telson with few spines, the former being somewhat square in transverse 

 section, and having distinct lateral ridges, (3) presence of exopodites on 

 the thoracic appendages, (4) third maxillipedes separated at their bases, 

 (5) absence of cervical groove ; and to these I may add others which seem of 

 importance, namely (6) character of the mandible, and (7) a fan-like group 

 of setse on the antennules, which may for convenience be referred to as the 

 " antennular screen." 



The changes which take place in these features in the transition to the 

 next stage are as follows : — 



(1) The Pleopods. 



The metamorphosis of the pleopods is shown in figs. 1 and 2, which are 

 camera lucida drawings of the last pleopod of the right side, showing the 

 cast cuticle, and the organ which has taken its place, both from the same 



Fig. 1. — Last pleopod of post-puerulus. Fig. 2. — Last pleopod of puerulus. 



ap.i., appendix interna; c.h., coupling Looks ; en., endopodite ; 

 ex., exopodite ; prot., protopodite. 



animal, it will be observed that the exopodite has become smaller, but the 

 chief reduction in size is in the endopodite and the appendix interna, both 

 of which undergo a reduction to about three-fifths of their former size. 

 A marked change is also observed in the plumose setfe, which cover both 

 sections of the limbs in the first stage, but are only found in the exopodite 

 in the next, the endopodite now being entirely devoid of them. The sinoie 

 long plumose seta, characteristic of the appendix interna, has also disappeared, 

 but the most marked change is in the complete disappearance of the couplii: o- 

 hooks (fig. 2, eh.). Examination of later stages shows that apparentlv both 

 in males and females the endopodite is similar, though in later stages the 

 endopodite of the female is larger and setose, while in the male it disappears 

 altogether. 



15' 



