246 
BULLETIN OF THE BUREAU OF 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 podobranchiae, 10 arthrobranchiae, 
and 4 pleurobranchiae, distributed according to the following table: 
Table 5. — Branchial Formula of the Lobster. 
The first larva has no rudiment of a podobranchia in the eighth somite, but all the 
other branchiae are represented. The podobranchiae of the following segments are very 
small and are partially exposed, together with their reniform epipodites (fig. 34). In the 
second larva the podobranchiae 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 anim.al and with its need 
of a greater respiratory surface, until it reaches between 30 and 40 in an adult 10}^ 
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. 
