PCEOILOSTOMA. 27 



secondly, that I sometimes, as, for instance, in LicJio- 

 molgus albens, found a small longitudinal, semi-pipe- 

 formed depression or groove exactly at the place where 

 the sipho of, for instance, Bijsjpontius and Ascomyzon is 

 inserted, and which I therefore considered to indicate 

 the place where the sipho and mandibles ought to be 

 found if any mandibles existed ; and thirdly and chiefly, 

 that sometimes, as in the genus Lichomolgus, the so- 

 called * maxillae ' are fixed on the ' mandibles ' (quite 

 as an ordinary palpus is fixed on a mandible or a 

 maxilla), and directed /rom the oral aperture, a cir- 

 cumstance with which I could find nothing analogous 

 in the class Crustacea, supposing Olaus' ' mandibles ' 

 really to be mandibles." 



The greatest difficulty which besets the discussion 

 of this question is the minuteness of the mouth-organs 

 in these animals, and the liability to displacement or 

 mutilation of the various parts in conducting a dissec- 

 tion, so that the organs of one and the same species 

 will often present very different appearances in differ- 

 ent preparations of the animal. There can be no 

 doubt, however, that the fact so strongly insisted on 

 by M. Thorell, — that of the coalescence, in Lichomolgus, 

 of the maxilla and mandible (or maxilla and palp) — does 

 really exist : the question remains. What is this palp- 

 like organ ? In appearance it is not unlike the poorly- 

 developed mandible- or maxilla-palp of many Grnathos- 

 toma, but it is also much like a single branch of such 

 a maxilla as we find in the genus Cycloiyicera or Arto- 

 trogus, so that not much can be leaimed by comparison 

 of structure only. The point next to be considered is 



