130 



of the fifth thoracic somite. All three flabella are richly 

 clothed with long setae. 



In the living animal the flabella have a slow motion 

 over the surface of the gills. Their main function is, 

 undoubtedly, to keep the surface of the gills free from 

 sand and mud which may be suspended in the water 

 carried into the branchial chamber. In a crab from Port 

 Erin the flabellum of the first maxillipede of the right 

 side had been destroyed. In consequence of this the 

 outer surface of the gills of the right side was covered 

 with a layer of fine mud, which must have rendered the 

 outer portions of the gills inoperative. It is doubtful 

 whether the flabella have any function with regard to the 

 formation or regulation of the current of water over the 

 gills. At any rate, this function, if present, has not the 

 importance ascribed to it by Claus.* 



The description of the respiratory mechanism of the 

 Brachyura given by Milne-Edwards has become almost 

 classic, and has been accepted by most workers on the 

 subject. According to this explanation, the water enters 

 the branchial chamber at one place, viz., in front of the 

 coxopodite of the chela. On entering the branchial 

 chamber the current passes backward below the gills and 

 then forward above the gills and out to the exterior 

 through the pre-branchial passage. 



This explanation has been disputed by Bohn,t who 

 states that the water enters the branchial chamber 

 throughout the entire length of the inner edge of the 

 sub-branchial region, the entrance being especially 

 marked at the anterior and posterior inhalent apertures 

 (" Porifice inspirateur anterieur et posterieur," Bonn). 

 According to Bonn, the water entering by the anterior 



* Glaus. Arbeit. Zool. Insiit. Wien, Bd. VI., Hft. 1. 

 t Bohn. Op. tit. 



