Structure of the Mouth in Sucking Crustacea. 299 



the lower ones not being developed into prehensile hooks. 

 Furthermore the middle lobes of the lower lip are quite 

 missing, and the foremost ones are so small, narrow, and 

 thin as to be unable to fill the space between the mandibles, 

 in consequence of which the palate here, as in Anonyx^ is 

 quite uncovered as soon as the maxillipeds and the two pairs 

 of maxillse are taken away. 



23. But the extremest place inside the boundaries of Eleu- 

 therognatha is occupied by the Icemodipodous Cyamus^ so 

 peculiar by its flattened shape, hooked legs, and general 

 equipment for attaching itself to the skin of whales, which it 

 gnaws to pieces and gulps down. The structure of its mouth 

 has been hitherto known only from the schematic outline by 

 Savigny. It will be seen from the following account what 

 considerable alterations in the shape and relative position of 

 the appendages of the mouth have been necessary, in order to 

 enable the animal to press the mouth against the extensive firm 

 surface which it has to penetrate and to which it must cling. 

 The usual arrangement of the organs (like strata, or leaves of 

 a book), by which the oral limbs generally in Amphipoda are 

 collected into a thick package under the head, has here been 

 abandoned, the most active instruments for gnawing (the man- 

 dibles and the first pair of m axilla) having been proportionately 

 expanded and flattened ; whilst tlie lower parts, which support 

 and enclose the former, viz. the second pair of maxillre and the 

 maxillipeds, are considerably reduced in development or pushed 

 out to the sides. Above all, the lower lip has lost the part 

 which it has to play in other Amphipoda, as in forming a 

 kind of spring for the mandibles ; so that it corresponds 

 entirely to the conformation of the tongue in Isopoda. Finally, 

 the equipment with spine and setge has almost entirely been 

 replaced by an equipment with organs of touch. 



The anterior extremity of the head presents a small oval 

 surface, surrounded, as far as the broad, shortly bilobate upper 

 lip, by the palpi of the maxillipeds, forming a sort of raised 

 margin when seen from above. These palpi are long and 

 stout, without claw, and consist of five joints, which only at 

 tlieir apices carry a few pointed setae, the last but one being 

 furnished at the apex with, a larger number of thin tactile 

 setfe ; some tactile warts are observable on the apex of the last 

 joint ; and this latter also has a small comb of delicate spines 

 on its inner margin. The broad, flat, almost quadrangular 

 stipites of the maxillipeds are so short that they only cover 

 the space behind the second pair of maxillai ; the lobes, more- 

 over, are entirely absent, or only represented by the slightly 

 expanded and rounded outer corners of the stipites, which 



