the Mouth in Sucking Crustacea. 3 



class of animals if it existed, and he suggests that perhaps the 

 jaws protrude during the suction in such a manner that they 

 may have been taken for a sucker*. Milne-Edwards has not 

 entered on the question, but merely given some figures of the 

 different parts of the mouth separately in ^ga, and a more 

 comprehensive series of illustrations of the mouth oiCymothoa'\, 

 some of which represent the parts in their natural connexion ; 

 all these figures are useful and good as far as they go, but 

 they do not go far enough. We might expect to find more 

 detailed information in Heinrich Rathke's anatomical essay on 

 j^ga hicarinata ; but he says that the organs of the mouth are 

 adapted for gnawing, and upon the whole constructed as in 

 Idothea. He adds, however, that the terminal part of the 

 mandibles is very hard, almost cuneiform, and strongly bent 

 downwards, and, further, that the orifice of the mouth is 

 remarkably small in proportion to the size of the animal. 

 These two last statements, which are quite correct in them- 

 selves, do not seem easily reconcilable with the first, viz. tliat 

 the mouth is adapted for gnawing, particularly as Rathke just 

 before says that the mandibles adhere to the head to such an 

 extent that their downward bent extremity cannot be capable 

 of much movement:]:. We shall nevertheless see, by-and-by, 

 that each of the authors named, Bosc, Latreille, and Rathke, 

 may be said to be right, to a certain extent. 



With regard to the structure of the mouth in masticating 

 Isopoda, we possess more ample information ; and the descrip- 

 tions and illustrations hitherto published, more especially 

 those contained in Milne-Edwards's excellent works, suffice to 

 give a tolerably complete idea of it. If, however, this infor- 

 mation is to serve us as a safe guide to the interpretation of the 

 sucking-apparatus of Gymotlioa and its related genera, it will 

 nevertheless be expedient to reconsider the subject once more, 

 and to place before ourselves a succinct analysis of the principal 

 types which may be observed in the structure of the mouth in 

 masticating Isopoda. We shall preface this analysis with a 

 few observations of a more general bearing. 



3. The limbs of Articulata are, in their origin, mere hollow 

 cylindrical prolongations of the skin, which are converted into 

 levers by the deposition of as many and as extensive layers of 

 chitine as the muscles of the animal require for their support, 

 and divided into as many separate pieces as the mode of loco- 

 motion requires joints. 



* Hist. Nat. des Crust, et des Ins. vii. p. 22. 

 t Le Regne Animal (ed. accomp. de pis.), pi. 65-67. 

 \ Nov. Act. Acad. Cebs. Leop.-Carol. Natur. Curiosor. t. xx. pt. 1, 1843, 

 pp. 26 & 27. 



