246 



BULLETIN OF THE BUREAU OP FISHERIES. 

 THE GILLS. 



The adult lobster is provided with 20 pairs of gills, i of which, belonging to the second 

 pair of maxillipeds, is rudimentary. Of these, 6 are podobranchise, 10 arthrobranchiae, 

 and 4 pleurobranchiffi, distributed according to the following table : 



Table 5. — Branchial Formula of the Lobster. 



ep.= epipodite. 



rud=rudiinentary. 



The first larva has no rudiment of a podobranchia in the eighth somite, but all the 

 other branchiae are represented. The podobranchise of the following segments are very 

 small and are partially exposed, together with their reniform epipodites (fig. 34). In the 

 second larva the podobranchise are covered by the carapace (fig. 41) and the branchial 

 formula is complete. 



The gills are developed in the embryo as simple folds or pouches in the body wall, 

 (fig. 8, g. fil.) They belong to the trichobranchiate type, the respiratory surface being 

 gradually increased by growth of multiserial branchial filaments. 



In the fourth larva the podobranchia carries four rows of filaments, and the 

 mastigobranchia, or epipodite proper, is a long, tapering, hairy plate. 



The adult gill (pi. xxxviii) , suggesting by its form a bottle brush, is a pyramidal tuft, 

 consisting of a central stem and numerous longitudinal rows of branchial filaments, which 

 enormously increase the area of the surface exposed to the water. The number of 

 rows of gill filaments gradually increases with the size of the animal and with its need 

 of a greater respiratory surface, until it reaches between 30 and 40 in an adult io>^ 

 inches long, while the total number of filaments in such a gill is between 3,000 and 

 4,000. The filaments are "parted" into two groups by a median longitudinal furrow 

 and in the larger posterior section tend by transverse partings to separate into quad- 

 rangular masses. The filaments gradually lengthen in passing forward or backward on 

 either side of the " part " and terminate in several rows of short filaments next the efferent 

 division of the stem, opposite the body wall. Further, the filaments are so regularly 

 spaced that they come to assume an arrangement in circular rows from base to apex of 

 the branchia, corresponding to the circular efferent vessels (fig. 2, pi. xlvii c v) with 

 which they communicate. 



