39 



the pulmonary vein, which is situated on the inner edge of the branchiae, 

 whilst the artery is situated on the outer edge. In the lobsters the 

 branchiae are constructed upon a different plan : they are somewhat 

 like those of the crabs in their outward configuration, but instead of 

 being composed of lamellae, they consist of a number of cylindrical 

 caecal tubes, attached by their base to the septum. They stand erect, 

 and are packed closely together side by side, like the bristles of a 

 brush, (Plate iv. figs. 1, 2, 3, 5, 6). 



In the crabs there are nine pyramidal branchiae on each side, two 

 of which may be said to be rudimentary, but in the lobsters there are 

 as many as twenty-two. The flabella, or sweeping organs, are three 

 in number, one on the upper row of the branchiae, one on the lower 

 row, and a third between the two rows, the latter is the shorter, (Plate 

 iii. fig. 6, whilst one of the others is represented by fig. 5). They are 

 of a flattened figure, and the hairs with which they are supplied are 

 attached to the sides principally, and also on the broad surface op- 

 posed to the branchiae, none being found on any other part, (Plate iii. 

 fig. 11). These hairs, as will presently be noticed, are of a peculiar 

 kind, differing in many respects from the hairs found in other parts 

 of the body of the animal. 



In speaking of the flabella in a preceding paragraph, it was stated 

 that their probable use was that of causing currents of water to play 

 constantly over the branchiae, and this appears to have been the view 

 entertained of their use by most authors who have devoted their atten- 

 tion to the subject, and amongst the most distinguished may be men- 

 tioned Cuvier, as advocating this opinion. In the ' Cyclopaedia of 

 Anatomy and Physiology,' article Crustacea, written by Milne 

 Edwards, the following passage occurs : — " In the greater number of 

 the Decapoda the flabelliform appendages of the maxillary or of the 

 ambulatory extremities penetrate into the respiratory cavity, and by 

 their motions as it were sweep or stroke the surface of the branchiae. 

 Some anatomists have even imagined, that it was by their action that 

 the water necessary to respiration was renewed in the interior of the 

 branchial cavities ; but this is a mistake ; these appendages have little 

 or no influence upon the current which is continually traversing the 

 respiratory antrum, and which is produced by the motions of the 

 great valvular lamina, already described as belonging to the second 

 pair of the maxillipedes, and situated in the efferent respiratory canal. 



"The very secondary part which the flabelliform appendages of the 

 thoracic extremities play in the interior of the respiratory cavities, is 

 of itself a sure indication of the indeterminateness of their numbers 



