BIOLOGY OF PHYSA 51 



Presumably the formation of the capsule about these slugs 

 took place in the same manner as that of the epiphragm of the 

 above named snails. As soon as the earth began to dry so that 

 the mucus about the slug began to harden, the animal retreated 

 away from it and a capsule was the result. Those that died 

 may have been the ones whose capsules had been ruptured 

 while the snails were withdrawing from the mucus. Some 

 of the land pulmonates, especially Helix, are known to form 

 an epiphragm during long hibernation. Several layers of mucus 

 are formed one within the other, with a greater or less space 

 between them. 



Dr. Binney (1878) after watching the process for some time, 

 described the formation of the epiphragm of Helix hortensis. 

 He says that the aperture of the shell was up and the collar 

 of the animal was brought level with it and a quantity of gelati- 

 nous matter was thrown out. The pulmonary orifice was then 

 opened, and a portion of the air wdthin suddenly ejected 

 with such force as to separate the viscid matter from the collar, 

 and to project it like a bubble of air from the aperture. His 

 description of the formation of the epiphragm of the land pul- 

 monate, Helix, refers presumably to the epiphragm formed 

 over the aperture of this snail during cold weather. In drought 

 I have observed that these snails form an epiphragm which 

 is very similar in appearance and is formed in the same way 

 as that of the fresh water pulmonate Lymnaea palustris. In 

 such a condition of drought the land pulmonate forms but a 

 single epiphragm which is frail and by no means always entire 

 and no mucus is shot out to project over the aperture like a 

 bubble, but the epiphragm is formed from the mucus left on the 

 foot when the animal ceases to crawl. Observations were made 

 of the formation of the epiphragms which Helix produce during 

 cold w^eather. They are found to be much thicker, have several 

 layers, and look as if they contained a substance like lime. 

 It is possible that this epiphragm may be formed by glands 

 different from those on the foot from which the drought epiph- 

 ragm is formed. 



III. Food and mucus correlated. 



There may be, as is suggested above, a constitutional differ- 

 ence in the viscosity of the mucus among the different genera of 



