Chap. I. NOCTURNAL. 13 



other hand he kept several large worms alive 

 for nearly four months, completely submerged 

 in water.* During the summer when the 

 ground is dry, they penetrate to a consider- 

 able depth and cease to work, as they do 

 during the winter when the ground is frozen. 

 Worms are nocturnal in their habits, and at 

 night may be seen crawling about in large 

 numbers, but usually with their tails still 

 inserted in their burrows. By the expansion 

 of this part of their bodies, and with the help 

 of the short, slightly reflexed bristles, with 

 which their bodies are armed, they hold 

 so fast that they can seldom be dragged 

 out of the ground without being torn into 

 pieces.f During the day they remain in 

 their burrows, except at the pairing season, 

 when those which inhabit adjoining burrows 

 expose the greater part of their bodies for 

 an hour or two in the early morning. Sick 



* I shall have occasion often to refer to M. Perrier's admirable 

 memoir, 'Organisation des Lombriciens terrestres' in 'Archives 

 de Zoolog. exper.* torn. iii. 1874, p. 372. C. F. Morren (' De 

 Lumbrici terrestris,' 1829, p. 14) found that worms endured 

 immersion for fifteen to twenty days in summer, but that in 

 winter they died when thus treated. 



t Morren, 'De Lumbrici terrestris,* &c., 1829, p. 67. 



