196 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



with the reflected lower edge of the carapace. Dissect the 

 membrane away and expose the gills. 



1. Each gill is pyramidal in shape, and is made up of a 

 series of leaflets, which are bound together by a tubular 

 stem, the vessel which carries venous blood to the gills. 



2. At the bottom of the gill-chamber notice a long, flat, 

 sword-shaped flap (w) fringed with hairs, the flabellum 

 of the first maxilliped. Separate the mouth-parts, and 

 seizing the base of the first maxilliped with a pair of for- 

 ceps, move the appendage, and notice that, as it moves, 

 the flabellum moves up and down over the outer surfaces 

 of the gills. 



3. Pass a bristle into the opening above the base of the 

 second maxilla, and notice that it passes into the branchial 

 chamber outside the bases of the gills. 



4. Underneath the external mandibular muscle notice a 

 smooth, transparent elevated, chitinous ridge, the exhalent 

 channel, through which the water passes away from the 

 branchial chamber. Notice that the bristle passes through 

 this channel. 



5. Turn the tips of the gills back, in order to expose 

 their inner surfaces, and notice that the lamellte are united 

 to each other by an internal hollow stem, the vessel which 

 carries the aerated blood down to the bases of the gills, 

 and then up to the pericardium. 



6. Notice that there is an internal branchial chamber 

 between the gills and the flancs. Pass a bristle into the 

 opening at the base of the third maxilliped, and notice 

 that its inner end projects into the internal branchial 

 chamber. 



7. At the bottom of this chamber notice a flabellum like 

 that in the outer chamber. Move the third maxilliped, 

 and notice that the inner flabellum moves at the same time. 



