PYCN0G0N01DEA. 



1389 



definite equatorial line, so to speak, from which to reckon in either 

 direction. Hence, in tracing the homologies in view, only parts pos- 

 terior to the mandibles, in one section of the Articulata, can corre- 

 spond to parts so situated in another section. On this account, the 

 upper lip need not be brought into our comparison, even were it a 

 transformed pair of appendages ; and for the same reason also, we 

 may doubt strongly its having this supposed relation, as it exists also 

 in Crustacea anterior to the mandibles, and notwithstanding the 

 various transformations which the other parts undergo, it retains 

 quite uniformly the same general character through all the grades of 

 species. 



There is also in Insects or Arachnida a languette, adjoining the 

 lower lip, which it has been suggested may be analogous to another 

 pair of maxillae. It seems more probably to be an appendage of the 

 lip, if not of the fleshy parts below, and has been so considered by 

 different entomologists. The lower lip itself is evidently a true pair 

 of maxillae, as the attached palpi present in Insects show. Yet it 

 does not follow that the lower lip in Crustacea has the same relations, 

 although having the same name. We have given reasons for reject- 

 ing this conclusion with regard to Crustacea in another place, where 

 we sustain the common view, that it is a mere fold of the skin. Ano- 

 ther strong reason for this opinion is found in Limulus, in which the 

 lower lip, instead of following, as usual, the mandibular legs, is situ- 

 ated posterior to the fifth pair of legs, the basal joint of all these legs 

 occupying the mouth opening. The lip, therefore, takes its position 

 from the character of the mouth, and is not fixed in position like a 

 pair of normal appendages. 



These remarks have been thought necessary to remove objections 

 that might come up, to the view we would present. The facts thus 

 lead us to conclude that the normal parts essential to the mouth of 

 Arachnida are but three pairs — a pair of mandibles and two pairs of 

 maxillae ; and this conclusion is essentially the same that is presented 

 by Latreille.* The number of organs in Arachnida, counting from 

 the mandibles, will hence be fourteen, the same number as in the 

 Pycnogonoids, and the two groups will be parallel, as follows : — 



* Cuv., Regne Animal, notes to General Remarks on Insects and Crustacea, and 

 Arachnida. 



348 



