The gills of Nephrons andamanica are attached on either side to the epimera 

 and appendages of certain of the thoracic somites. The space on either side in 

 which they lie is known as the gill-chamber : its inner wall is formed by the 

 epimera of the thoracic somites, its outer wall is formed by the side-wall of the 

 carapace, or hrancliiostegite. 



In respiration water is drawn under the edge of the branchiostegite into 

 the branchial chamber, and streams forwards over the gills, until it passes out 

 again between the anterior edge of the branchiostegite and the epistome, the 

 current being maintained chiefly by the movements of the scaphognathite, 

 already described in connexion with the 2ud maxillfe. 



There are twenty gills on either side, though the most anterior of them, 

 which is attached to the 2nd maxillipeds, is a rudiment. 



They are arranged in three series in either branchial chamber : those of 

 the outer series, which with the epipodites are attached to the coxopodites of 

 the appendages, are known as podohrancUas ; those of the middle series, which 

 are attached to the membranes that connect the coxopodites with their somites 

 are known as artlirohranch'm ; while those of the inner series, which are attached 

 to the epimera of the somites, are known as phmrolrancMse. 



The podobranchise are six in number on either side, including the rudi- 

 mentary one, and are attached one to each of the following appendao-es : the 2nd 

 maxillipeds (rudiment), the external maxillipeds, and the first four thoracic legs. 



The arthrobranchiffi are ten on either side, and are attached in pairs to the 

 external maxillipeds and the first four thoracic le^s. 



The pleurobranchiaj are four on either side, and are attached to the epimera 

 of the last four thoracic somites. 



The number and disposition of the gills is expressed in the following 

 branchial formula., in which the thoracic somites are numbered in serial succes- 

 sion to the six somites of the head : — 



The Branchial Formula of Nephrops andamanica. 



