166 JUNE. 



during life, but if it is capable of being wholly everted, 

 as in many species, these teeth must be turned on the 

 outside, where they would seem to be of little use. 

 Possibly, however, the e version may be only just suffi- 

 cient to bring these teeth to the margin, when their 

 action might be made very efficient by the slightest 

 alteration in the contraction of the sac. 



Some species of this genus construct for themselves 

 enveloping tubular cases, out of mucus given off from 

 their bodies, and fragments of shells. In these they 

 ordinarily live concealed, but are sufficiently active 

 when they leave their houses. Some shine with a 

 phosphorescent radiance in the dark. 



In the great class of Worms, special organs for loco- 

 motion are often altogether lacking ; and, where found, 

 are only rudimentary. Alternate swellings and con- 

 tractions of certain portions of the body are a great 

 source of progression ; and these are effected by the 

 fluids of the interior, which are driven to a given part 

 of the cavity, and momentarily imprisoned there by the 

 contraction of the circular tegumentary muscles before 

 and behind it ; the body swelling at that place. " The 

 muscles of the integument are then excited to action, 

 and the fluid is forcibly compressed forwards or back- 

 wards, according to the direction of the muscular agency. 

 Nearly all Annelids are struck with paralysis when this 



