CARIDEA. 



273 



still altogether wanting. In the second antenna, the transformation 

 of the exopodite into the scale and of the endopodite into the 

 nagellum of the adult can be recognised, the mandibular palp is 

 wanting as well as the leaf-like appendage (exopodite) of the first 

 maxilla, which is found in Penaeus. The heart has two pairs of 

 ostia, a normal condition in the Zoaea, the third pair developing 

 during the Mysis stage. 



While an apparent irregularityjjs produced in the order of 

 development of the segments by the suppression of the fifth thoracic 

 segment, the rudiments of the limbs appear in the regular order 



FIG. 125. Older larva of Hippolyte, after the development of the thoracic appendages (after 

 CLAUS, from BALFOUR'S Text-book). 



from before backwards. The only exception is afforded by the 

 sixth pair of pleopoda, which frequently develop precociously. The 

 ambulatory limbs develop gradually from before backwards, in 

 contrast with those of the Sergestidae and of Penaeus, which appear 

 simultaneously. The development of the thoracic limbs frequently 

 shows variations in detail which are not all as yet accurately known. 



In Hippolyte, the first two pairs of ambulatory limbs and the sixth pair of 

 abdominal limbs (uropoda) appear simultaneously. In an older stage (Fig. 125) 

 these become biramose, while the buds of the three posterior pairs of ambulatory 

 Hmbs also appear. In Palaemon, the larva which hatches from the egg has 

 the rudiments of the three following thoracic limbs developed behind the third 

 pair of maxillipedes (BOBRETZKY). The larva of Crangon, when hatched, shows 

 the bud-like rudiments of the two anterior pairs of ambulatory limbs ( GLAUS, 

 No. 113 ; EHRENBAUM, No. 123*), but the rudiments of the three following 



* G. O. SAKS (No. 151), on the contrary, states that in Crangon vulgaris and 

 in Cheraphilus and Pontophilus only the buds of the first pair of ambulatory 

 limbs are present, while the four remaining pairs appear simultaneously in the 

 next stage. 



