24 OMENSETTER : 



secreted by means of their mantle, and which is perforated by 

 a small hole to admit the air. In Winter they bury themselves 

 with the head upwards and do not grow at all during that 

 time. While increasing in bulk they bury themselves in 

 Summer at intervals for several days, with the head down-, 

 wards, meanwhile growing rapidly. 



In dry weather and during the heat of Summer snails also 

 close their shells to protect then-selves from drought, but this 

 covering is thinner than that which they construct in Winter. 



It is said that in the British Museum is preserv^ed the shell 

 of an Egyptian snail which revived after having been gummed 

 to a board for four years in the Museum, and lived two years 

 afterward. Other instances of the revival of land mollusks 

 after a still longer period are equally well authenticated. 



Some species retire to Winter quarters earlier than others, 

 and their pulsation, which ranges from 30 to no during the 

 Summer, ceases entirely in these creatures throughout the 

 reign of cold. Slugs likewise bury themselves in the ground 

 and become torpid during frosts and droughts, but it is ques- 

 tionable if their condition is that of genuine hibernation. 

 Slugs differ from snails in not being protected by a shell. 



The fresh water mussels hibernate before the close of 

 Autumn and cover themselves in the mud until the beginning 

 of Spring. They have been observed traversing the beds of 

 our creeks as soon as early March. 



It is believed that many of the marine mollusks hibernate, 

 but very little is known of their habits at this time. 



Most of the insects which pass the Winter as larvae or per- 

 fect insects become torpid during the period when food is not 

 to be obtained. Larvce which are full grown in Autumn fre- 

 quently lie dormant during the Winter and do not assume the 

 pupa state till Spring. In the case of insects which have 

 more than one brood in the year, the last brood generally 

 hibernates, sometimes retiring to Winter quarters quite early 

 in Autumn, while the perfect insects of the previous brood are 

 still flying about and while the weather is yet fine and warm. 



