On the Oral Folds in the Shells o/" Clausilia. 209 



In favour of at least the partially respiratory function of 

 their ventral sacs, the feeble development of the tracheae in 

 the above-mentioned Diplopoda and Collembola may be cited ; 

 in the latter the ventral tube, which is often very extrusible, 

 corresponds to the first pair of ventral sacs of the Thysanura, 

 and stigmata occur at the utmost (Sminthurus) on the 

 anterior margin of the prothorax. Further in favour of this 

 function is the fact of the deficiency of the ventral sacs in 

 those Thysanura which possess a more highly developed 

 trachea] system of the Orthopterous type, with strong ventral 

 longitudinal trunks, such as Japyx gigas and solifugus, 

 Lepisma (and Lepismina?). On the first abdominal segment 

 of Japyx, the decidedly glandular function of the ventral sacs, 

 as in the Chilopoda, which, according to H. Eisig (L c. 

 p. 392), is to be regarded as the primitive one, has apparently 

 alone persisted. Any special glandular functions of the 

 ventral sacs in other forms still need more accurate observa- 

 tions, which the author hopes to make very shortly. 



That in reality the ventral sacs, of the Collembola for 

 example, perform other functions is rendered probable by 

 some observations upon the living animal, the results of 

 which, however, are contradictory ; thus Nicolet, Olfers, 

 Lubbock, and Tullberg ascribe to the ventral tube the action 

 of an adherent organ, while O. Reuter regards it as an 

 arrangement for the reception of water ; in Macrotoma, again, 

 A. Sommer has described large, unicellular glands, opening 

 by a pore. 



The ventral sacs of Machilis also show upon the dorsal 

 surface a special glandular epithelium of much thickened, 

 sharply defined cells, the plasma of which breaks up into 

 fine, close cords, just as has been demonstrated by A. Weis- 

 niann and 0. Grobben for the excretory antennal glands of 

 the Crustacea. 



XX VIII. — On the Nomenclature of the Oral Folds in the Shells 

 of Clausilia. By Edgar A. Smith, F.Z.S., and B. B. 

 \Voodwakd, F.G.S. 



[Plate XI. A, figs. 1-4.] 



It is well known to all conchologists that among the distin- 

 guishing features of the genus Clausilia the folds (plicce and 

 lamella? as they are variously termed) within the aperture or 

 mouth of the shell are especially characteristic. 



