266 



THE SLIT — THE TUBED OPERCULATES 



serve the purpose of admitting water to the branchiae, while 



others are anal. In Troehotoma 

 there are only two holes, united by 

 a narrow fissure. 



The Tuhed Land Operculates. — 

 Agroupof the Cyclophoridae, which 

 is restricted to Further India and 

 the great Malay Islands, has devel- 

 oped a remarkable sutural tube on 

 the exterior of the last whorl, near 

 the aperture, A similar tube, but 

 more obscure, exists in Alycaeus. 

 Several stages in the development 

 of this tube may be noticed, begin- 

 ning with the elevation of part of 

 the peristome into a simple irregu- 

 lar shelly plate, which is continued, 

 first into a short, and then into a long tube, which becomes 

 soldered to the shell ; finall}^ the tube becomes free, and the 

 anterior part of the last whorl is disconnected from the spire 

 (Fig. 180 A-D). 



It is singular that the tube does not appear to be of any use 

 to the animal, since its internal extremity, in the complete form, 



e D 



Fig. 179. — The slit in A, Bellerophon, 

 B, Fleuroiomaria, C, Schismope, 

 D, Polytremaria, E, Haliotis (not 

 (irawn to scale) . 



Fig. 180. — Development of the tube in the tube operculates: A, Pterocycus rupestris 

 Bens. ; B, Opisthoporus birostris Pfr. ; C, Spiraculum travancoricum Bedd. ; D, 

 Rhiostoma Housei Pfr. 



is closed, and does not communicate with the interior of the 

 whorl. It may be presumed, however, that in origin the tube 

 served as a means of conveying air to the animal when the 

 operculum was closed. The holes in the peristome of Pupina^ 

 Cafaulus^ and Anostoma (Fig. 154) may be compared. 



