406 



GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



back directly to the ancestral ISTauplius, tlie common ancestor of all tlie 

 JS'eoccirida. 



Nor does it seem to us that tMs statement or hypotliesis is weakened 

 wlieu we consider the resemblauces between the thoracic feet of the 

 Phyllopods and the maxill* and maxillipedes of the Decapoda. When 

 we comp ire the leg of a Phyllopod with the 

 second maxillffi* of the lobster or cray-fish, we 

 can detect a close homology, the chief difference 

 being in the fact that the lobes of the endopo- 

 dite are less numerous in the Decapod than in 

 the Phyllopod. This close resemblance is based 

 on the fact, which appears to have been over- 

 looked by Claus and Lankestei", i. e., that, as in fig. 29.— MamiMe of the lobster, 

 the Phyllopodous limb, the maxillai of theDgf ^o"»»'-«««»*^™«»"^-^«''P^^p"'^- 

 capods have no jointed axis, the limb consisting of epipodal and endo- 

 podal portions alone, the stem or axis being wanting. In the maxillipedes, 

 where part of the endopodal region of the limbs becomes, as Lankester 

 claims, two multiar- 



A. 

 flab/, 



,jj^- 





flxib 



:^eTV 



hp 



ticulate endites, the 

 fifth and sixth ; or, as 

 in the thoracic leg, be- 

 comes a single seven- 

 jointed endite, the 

 homologies cannot 

 with certainty be 

 traced. The lobster's 

 thoracic leg consists 

 of the iointed axis , . , .„,.■, 1 . a ^■, ■,. ^ ■ ^■■>■ 



, . , -J.! 1 ricx. 30.— A, first maxilla of lobster; «2, endopodite; 6^, basipodite; 



WillCll IS tne ilOmO- y?a&, Aabellum. B, .second maxilla gf lobster; hp, basipodite (epifiDa- 



lno-nf> of nprhin>^ the thus) ; ca;p, coxopodite. (This appeiitacre, with its five eudopodal lobes, 



n,i?l 1.:^ V Jr approximates nearest to the Phyllopod limb.) 



filth endite of the 



Phyllopodous foot, and the complicated gills and gill-fan (scaphogna- 



thite) correspond to the gill and flabellum of the Phyllopodous leg or 



fiabellum. 



In brief the maxillse of the Decapoda most 

 closely resemble the leg of Phyllopods. The 

 maxillipedes, for example those of the third 

 pair, are much more diiferentiated than the 



flah 



flab 



cozp 



riG. 31.-C, first masilUpede of lobster. Tig. 32.-D second maxillipede ; ex, 



' ^ esopodite; md.endopodite ;/«?), epipo- 



dite or flabellum, or scaptogathnite. 



limbs of the Phyllocarida or Phyllopoda. In the Decapoda the gill and 

 flabellum are homologous with those of the groups just enumerated; 



* The resemblance to the second maxilliB of the young lobster in its first stage when 

 freshly hatched is still more striking. See Smith's Early Stages of the American 

 Lobster, PL XVI, fig. 4. 



