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 of Cymothoaf, 
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 
Aiga bicarinata; 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. that 
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 movementt. We shall nevertheless see, by-and-by, 
that each of the authors named, Bosc, Latreille, and Rathke, 
ee said to be right, to a certain extent. 
ith 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 Cymothoa 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. 
Tt Le Régne Animal (éd. accomp. de pls.), pl. 65-67. 
} Noy. Act. Acad. Cees. Leop.-Carol. Natur. Curiosor. t. xx. pt. 1, 1843, 
pp. 26 & 27. . 
1* 
