l68 THE DISPERSAL OF SHELLS. 



selves by forming a kind of cocoon "secreted from their 

 skin and often mixed with earthy and extraneous par- 

 ticles " : the " nest of earth " made by T. maugei in 

 times of drought, it is said, reminds the observer of the 

 cocoon of the puss-moth ; within, the animal lies 

 encysted until moisture, finding its way through the 

 walls, rouses it again to activity. While in the encysted 

 state ^' a thin white membrane (a development of the 

 mantle) is extended from beneath the shell and stretched 

 over the back and sides of the animal/' checking evapora- 

 tion, and forming an admirably-designed protective 

 shield.^ The Testacclla's power of retaining life under 

 adverse conditions is well illustrated by observations 

 made by Professor Poulton in 1886: — 



'' Between four and five months ago I found eleven 

 specimens of this slug [Testacella, species not stated] 

 upon a low wall surrounding the garden of a house 

 near the Oxford University Parks, and on the following 

 day I captured eleven more in the same place. ... A 

 few of the twenty-two specimens were killed and 

 hardened, and the remainder were put in a box con- 

 taining earth, in which they buried themselves. In the 

 press of other work the box was neglected, and re- 

 mained untouched in my laboratory until to-day 

 [October 19th], the earth having quickly dried into a 

 hard cake. To-day I emptied the box, and fully ex- 

 pected to find the slugs dried up dead, but to my 

 surprise I found twelve specimens alive, each encysted 



' "British Conchology," i. (1S62), pp. 143, 147-S. 



