462 PHYLLOPODA. 



larva (fig. 208 B) loses its oval form, mainly owing to the elong- 

 ation of the hinder part of the body and the lateral extension of 

 the cephalic shield, which moreover now completely covers over 

 the head and has begun to grow backwards so as to cover over 

 the thoracic region. At the second ecdysis there appears at its 

 side a rudimentary shell gland. In the cephalic region two 

 small papillae (fr) are now present at the front of the head close 

 to the unpaired eye. They are of the nature of sense organs, 

 and may be called the frontal sense papillae. They have been 

 shewn by Claus to be of some phylogenetic importance. The 

 three pairs of Nauplius appendages have not altered much, but 

 a rudimentary cutting blade has grown out from the basal joint 

 of the mandible. A gland opening at the base of the antennae 

 is now present, which is probably equivalent to the green gland 

 often present in the Malacostraca. Behind the mandibles a pair 

 of simple processes has appeared, which forms the rudiment of 

 the first pair of maxillae (mx). 



In the thoracic region more segments have been added 

 posteriorly, and the appendages of the three anterior segments 

 are very distinctly formed. The tail is distinctly forked. The 

 heart is formed at the second ecdysis, and then extends to the 

 sixth thoracic segment : the posterior chambers are successively 

 added from before backwards. 



At the successive ecdyses which the larva undergoes new 

 segments continue to be formed at the posterior end of the body, 

 and limbs arise on the segments already formed. These limbs 

 probably represent the primitive form of an important type of 

 Crustacean appendage, which is of value for interpreting the 

 parts of the various malacostracan appendages. They consist 

 (fig. 209) of a basal portion (protopodite of Huxley) bearing two 

 rami. The basal portion has two projections on the inner side. 

 To the outer side of the basal portion there is attached a 

 dorsally directed branchial sack (br) (epipodite of Huxley). The 

 outer ramus (ex) (exopodite of Huxley) is formed of a single plate 

 with marginal setae. The inner one (en) (endopodite of Huxley) 

 is four-jointed, and a process similar to those of the basal joint 

 is given off from the inner side of the three proximal joints. 



At the third ecdysis several new features appear in the 

 cephalic region, which becomes more prominent in the succeeding 



