THE VALKERIA IMBRICATA. 101 



one, /, arising from the lower part of the tube, and 

 inserted into the upper part of the gullet ; the other, 

 #, into the bottom of the stomach. But besides 

 these muscles, there is a set connected with the 

 tentacular apparatus, for closing them up ; in order, 

 however, to understand how this is effected, we must 

 attend more minutely to the cell itself. 



The cell may be divided into three portions : 

 1. A basal, horny, transparent portion, firm and 

 unyielding. 2. A soft, flexible continuation ; and, 

 3. A marginal circle of bristle-shaped appendages, 

 connected like the rays on the fins of a fish by a 

 most delicate tissue. 



When the animal withdraws itself, the arms are 

 first folded up into a close bundle, and then retracted; 

 the gullet being drawn down at the same time. 

 With the descent of the ossophagus the soft part of 

 the tube begins to be inverted, and the setce, or 

 bristles, gradually close together. These are then 

 drawn inwards till they disappear, the soft tubular 

 part forming a sheath around them, the whole con- 

 stituting a sort of stopper, shutting up the animal in 

 its horny case. The muscles by which this retrac- 

 tion of the tentacles is effected, are six in number ; 

 they arise from the horny part of the shell, and 

 are inserted into its flexible portion, on which 

 they act. 



How marvellous are the facts on which we are 

 dwelling ! Well may they lead us to say with 

 Fenelon : " my God, he who does not see thee 



