42 



the flabella are of a flattened figure (PI. iv. figs. 9, 10), much broader 

 than the branchiae, and their edges, as well as both of their flattened 

 surfaces, are covered with spines and with spiny hairs. The flabella 

 are so placed between the branchiae, that their broad surfaces are in 

 immediate contact with the broad surfaces of two branchiae, and as 

 they are in constant movement, the effect produced must be like that 

 of one brush being rubbed upon another, whereby all the tubes in 

 succession are brought in contact with the surrounding fluid. Some 

 of the hairs from these flabella are represented in Plate iv. figs. 12, 

 13, 14, 16, and the one represented by fig. 17, which is from the 

 large cray-fish, is peculiarly adapted to the required office. Several 

 other species of Crustacea have been examined, but all with the same 

 result, nothing materially different having been found about their 

 branchiae to warrant a special description. 



If the view that has been taken of the use of the flabella be the cor- 

 rect one, and indeed, all that can be seen would warrant such a con- 

 clusion, we have before us another instance of the great value of the 

 microscope in anatomical researches, and an unquestionable proof 

 that the aid of an assisted sense is often requisite to unravel some of 

 the apparent mysteries of Nature, which mysteries show the more 

 strikingly contrivance and design, the more deeply and carefully 

 they are investigated. 



