Crustacea. 7655 



their food in a bundle often as big as themselves. " It is amusing," 

 he says, " to see the ci-abs sitting, as it were, upright, to cut their way 

 with their sharp pincers, and then waddling off with their sheaf within 

 holes, as quick as their sidelong pace will carry them." It appears 

 absolutely necessary that they should dwell where moisture is abundant, 

 in order that the branchial organs may have the surface kept damp, 

 for they appear not otherwise to be endowed with the capability of 

 absorbing the oxygen from the surrounding atmosphere. 



The apparatus by which the oxygen is brought into contact with 

 the blood consists of a series of very thin flat plates, laid side by side 

 and strung together by the middle from the upper to the lower edges. 

 Through the central column flows in, at the lower margin, the impure 

 blood, which is returned again along the upper in an invigorated 

 state, having in the meantime passed into the thin lateral plates, 

 between which the water in marine and the air in terrestrial Crustacea 

 passes ; these plates are kept asunder by moisture and a peculiar appa- 

 ratus that was first pointed out to me by Prof. Quekett. Each plate 

 upon the upper margin has one or two small prominences, unimportant 

 in each individual specimen, but in the aggregate the manv form one 

 or two considerable ridges traversing the entire column. Each 

 branchia is an appendage to one of the limbs. The two anterior pairs 

 of these limbs are in these crabs formed so as to be appendages 

 immediately attendant upon the mouth ; to one of these the branchial 

 organs, instead of being developed into a true branchial column, is 

 formed into a long flat lash, flexible and sweeping, arranged so as to 

 overlie the branchias : this flabella has the edges fringed with long 

 hairs, each of which is notched with many small teeth. The mem- 

 brane lining the branchial vault is similarly furnished. The hairs 

 upon the long flabella, as it sweeps the surface of the branches, hitch 

 their teeth in the prominent ridges and separate each of the plates 

 from contact with its neighbour, and thus facilitate the more perfect 

 action of the fluids. 



But as we descend from those in which the blood flows through 

 canals adapted for the purpose, to others where it merely passes 

 through channels between the muscles, we find that the organs 

 adapted to aerate the blood is of a less complex character. In the 

 Amphipoda and some of the Stomapoda they consist of a series of 

 single chamber-cells, analogous in character to that of a single plate 

 of the more perfect organ, and to which they bear a complete resem- 

 blance when in a larval condition. 



In the Isopoda we have a broad demarcation. In all the previous 



