No. 6 (1921) COMMON MOLLUSCS OF SOUTH INDIA 197 



supposed to be of use in protecting their owner against the intru- 

 sion of any unwelcome visitor. These pallets may be likened in 

 function to the operculum of a gastropod. 



Last of all and more degenerate and quite unlike the typical 

 bivalve are the WATERING-POT SHELLS {Claoagellidae). They 

 are common on our shores, washed up after storms; they may 

 also be found at very low tides embedded upright in the sand. In 

 form their shells are short, stout brittle cylinders about three inches 

 long with several delicate upstanding frills round the open or upper 

 end. The lower extremity is closed, slightly convex, perforated 

 with holes and fringed with a number of short open-ended 

 tubes — the whole suggestive of the rose of a watering-pot, whence 

 the name. When seen first, the impression is that the short open 

 cylinders fringing the "rose "are the broken bases of root-like 

 tubes ; this is not the case. That the creature is a bivalve is seen 

 not only by a study of the soft parts of the body, but by the 

 presence of a tiny but perfect bivalve shell embedded in the 

 surface of the main tube just above the " rose." The larger 

 structure, the frilled cylinder, is a secretion of the siphons. 



A common Indian species is Brechitcs didiotonius or Aspcrgillum 

 dichotomiDii as it was formerly called. 



CLASS v.— CEPHALOPODA. 



The Cephalopods are so called because the foot, here divided 

 into a number of tentacle-like arms, is attached apparently to the 

 head. The body is a muscular sac containing the viscera and 

 gills. In many forms an internal " bone " or "pen" stiffens the 

 body in a manner comparable with the backbone of the higher 

 animals. The head, joined to the body by a narrow neck, is 

 furnished with a pair of large eyes, perfectly constructed optically 

 but evolved by quite a different line of development to the 

 vertebrate eye. The arms, eight to ten in number, arise in a circle 

 at the fore-end of the head. Except in the case of the Pearly 

 Nautilus, these are armed with a large number of suckers, enabling 

 the animal to cling tenaciously to any object. Each sucker is a 

 round disc with a little bulbous cavity at the centre that enables 

 the creature to work the sucker apparatus like an air-pump; the 

 vacuum created causes the sucker to adhere by atmospheric 

 pressure and this continues so long as the central intelligence 



