Chap. VI. STIIUCTUEE OF THE HEAET. 39 



CHAPTER YI. 



STEUCTÜKE OF THE HEART IN THE EDEIOPHTHALMA. 



Scarcely less striking than the example of the air- 

 breathing Crabs, is the behaviour of the heart in the 

 great section Edriophthalma, which may advantage- 

 ously be divided, after the example of Dana and Spence 

 Bate, only into two orders, the Amphipoda and the 

 Isopoda. 



In the Amphipoda, to which the above-mentioned 

 naturalists correctly refer the Caprellidae and Cyamidae 

 (Latreille's Lwmodiiooda) , the heart has always the 

 same position ; it extends in the form of a long tube 

 through the six segments following the head, and has 

 three pairs of fissures, furnished with valves, for the 

 entrance of the blood, situated in the second, third, 

 and fourth of these segments. It was found to be of 

 this structure by La Yalette in Ni^pliargus {Gammarus 

 ^uteanus), and by Claus in Phronima ; and I have 

 found it to be the same in a considerable number of 

 species belonging to the most different families.^ 



1 The yoimg animals in the egg, a little before their exclusion, are 

 usually particularly convenient for the observation of the fissures in the 

 heart ; they are generally sufficiently transparent, the movements of the 

 heart are less violent than at a later period, and they lie still even 



