THE MOLLUSCA 105 



to the back of another, are formed, the chain often consisting of 

 twelve or more individuals. 



" Crepidula is a protandric hermaphrodite that is to say, all 

 the individuals are born as males, and, passing through an appar- 

 ently hermaphrodite stage, change into females. Consequently 

 chains are formed in the following manner : 



" The young male individuals creep about from place to place, 

 and eventually settle down either on a shell or some similar surface, 

 or at the end of a chain. Suppose an individual to settle on an 

 oyster shell. The young male grows larger, and at the time th, 

 edge of its shell takes on the contour of the surface to which it 

 is attached, so that they fit accurately together. As the individual 

 increases in age, it begins to change into a female, another young 

 male in the meantime having crept on to its back. With a repe- 

 tition of this process, longer and longer chains are formed, until 

 in odd cases as many as thirteen individuals may be found in 

 chain. In this way it will be seen that in any chain the bottom 

 individuals will be females and the end individuals males, while 

 between these may occur individuals of all intermediate sex forms 

 between male and female." l 



The Slipper Limpet made its appearance in England in about 

 1880, probably being introduced with imported American oysters, 

 on Which it is fond of fixing itself, and in some places the Crepi- 

 dulae have multiplied to such an extent that they have become 

 a troublesome pest to oyster fisheries. 



The Cowries are an interesting family of carnivorous Gastropods, 

 for the most part inhabiting the tropic seas. They are distinguished 

 by the varied markings and wonderful polish of the shells, the 

 enamelled surface being produced by the action of two flaps of 

 the mantle, one on either side, which turn back over the shell and 

 meet together in the centre. 



The animal inhabiting the shell is most brilliantly coloured; 

 it has no operculum, and its foot is so large that it appears remark- 

 able that it can so easily be protruded and withdrawn through 

 the narrow, slit-like aperture which distinguishes the Cowry shell. 

 Cowry shells are used as ornaments by many savage tribes, and 

 the large Orange Cowry is worn as a mark of high rank by the 



1 J. H. Orton, B.Sc., Journal of the Marine Biological Association. Vol. ix., 

 No 3, p. 437. 



