196 



THE APOBID^E 



PART II 



him fused with one another and with the basal plate, 

 but still distinct. On the well-known principle of the 

 increase of the respiratory surface by the formation 

 of integumental folds, the dorsal (i.e. morphologically 

 posterior) surface of the gills has developed a row of 

 leaf-like folds. 



It is of importance to note that it is only that part 



WSmm \ K I X^ 



g 



d 



FIG. 45. One of the abdominal limbs of Limulusto? comparison with a Phyllopodan 

 limb. ?', ventral parapodla fused together; d, dorsal parapodia (endopodites) ; 

 jl, flabellum or sensory cirrus (exopodite) ; -, gill, the posterior surface of which 

 carries leaf-like integumental folds. 



of the limb of Limulus which morphologically cor- 

 responds with the gill of the parapodium (or of the 

 Phyllopodan leg) which is thus modified. One would 

 have been inclined to think that the increase of the 

 respiratory surface could have been better obtained 

 by using the whole surface of these leaf-like limbs. 

 We have here a most interesting case of the strict 

 localisation of function. The increase of respiratory 



