40 LEPADIDJE. 



swollen or bullate, often to such an extent as to equal 

 in its longitudinal axis the rest of the mouth ; of palpi 

 soldered to the labrum ; of mandibles, maxillae, and outer 

 maxillae, the latter serving as a lower lip. These organs 

 have only their upper segments free, but there are traces, 

 clearly seen in the mandibles (PL X, fig. 1, a, b), of their 

 being formed of three segments. The two lower seg- 

 ments are laterally united, and open into each other, the 

 prominence of the mouth being thus caused : this condi- 

 tion appears to me curious, and is, to a certain limited 

 extent, intermediate between those articulated animals 

 which have their tropin soldered into a proboscis, and 

 those furnished with entirely free masticatory or prehensile 

 organs. The palpi adhere to the corners of the labrum ; 

 and I call them palpi only from seeing that they spring 

 laterally from above the upper articulation of the man- 

 dibles. The prominence of the mouth, measured from 

 the basal fold by which the whole is separated from the 

 body, is much greater on the half formed by the labrum 

 and mandibles, than on the other half facing the cirri. 

 The tropin surround a cavity — the supra-cesophageal 

 cavity — in the middle of which, between the mandibles 

 is seated the orifice of the oesophagus. The oesophagus 

 is surrounded by long, fine, muscular fasciae, radiating in 

 all directions, opposing the constrictor muscles, and is 

 capable of violent swallowing movements, — constriction 

 after constriction being seen to run down its whole 

 course : there are also some fine muscles attached to the 

 membrane forming the supra-cesophageal cavity. The 

 trophi serve merely for the prehension of prey, and not 

 for mastication. 



The Labrum, as stated, is always bullate or swollen ; 

 and sometimes the upper exterior part forms, as in 

 Ibla (PI. IV, fig. 8 a, c), and Dichelaspis, an overhanging 

 blunt point. The object, I suspect, of this bullate form 

 is to give, in the upper part, attachment to longer muscles 

 running to the lateral surfaces of the mandibles, and 

 lower down to the oesophagus. The crest close over the 



