FIRST ZOEA OF PORCELLANA. 61 



The mandibles and maxilla? are shown before the moult in 

 Plate VII, Figure 7, and after the moult, in Plate VI, Figures 3, 

 4, and Plate VII, Figure 5. 



In the first stage, Figure 7, Plate VII, these three appendages are 

 folded together, and covered by the embryonic skin which is nearly 

 conformable to their surface, although, as shown by the light outer 

 line in the figure, it does not follow all the folds. No trace of a 

 palpus could be discovered on the mandible, and the hairs at the 

 tip of the maxillse were almost completely invaginated into the 

 appendages. 



After the moult these three pairs of appendages become func- 

 tional, and have nearly the adult character. The mandibles, 

 Plate VII, Figure 5, and Plate VI, Figure 6, M, are not exactly 

 alike, but exhibit that slight departure from bilateral symmetry 

 so frequently found in these appendages. No trace of a mandibular 

 palpus could be found, although there was a small area where the 

 integument had been broken in each of the two specimens which 

 were dissected ; and as this area, shown in the figure, was at the 

 same place in both cases, the fracture may have been produced by 

 the removal of a palpus. 



The first maxilla, Plate VI, Figure 3, and Figure 6, MX, consists 

 of a two-jointed basal portion, a, 6, with stout cutting hairs, and a 

 slender endopodite c, which in one specimen ended in two, and in 

 another specimen in three long, slender, irregularly plumose hairs. 

 The distal joint, 6, of the basal portion carries upon its cutting 

 edge, one row of five stout spines and a second row of four slender 

 spines parallel to the larger ones. In the specimen figured, the 

 proximal joint, a, was twisted so that its inner surface was shown, 

 and the posterior edge is therefore the one at the left of the figure. 

 It carries five long, stout, plumose spines, and at the posterior 

 angle of its cutting edge a single spine without secondary hairs. 

 No trace of an exopodite or scaphognathite could be detected in 

 this appendage. 



The second maxilla, Plate VI, Figure 4 and Figure 6, MX', con- 

 sists of a three-jointed basal portion with short stout hairs; a two- 

 jointed endopodite, b, with longer hairs ; and a long flat exopodite, 



c, with five long hairs at its distal, and a long plumose flagellum, 



d, at its proximal end. 



In the first stage, the first and second maxillipeds, Plate VI, 

 Figure 1, Mp, Mp' } are fully developed, although the presence of 



103 -,. 



