101 



along the back of it, and are inserted into the head. They draw the 

 ganglion upward or to either side. To the lower part of the sac are 

 attached two pairs of thick and strong muscular cords, which pass 

 down to the hinder extremity of the body ; one pair are fastened to 

 the sides (10, 10), and the other pair (9, 9) somewhat on the ventral 

 aspect of the sac ; the latter are particularly stout and powerful. 

 Their action is, doubtless, to draw back the sac into the trunk, an 

 operation continually being performed, though I know not its object. 

 Often in the sudden driving back of the sac, these stout strings are 

 seen bent into a sigmoid curve ; this might seem to militate against 

 their being muscles ; but, I think, when thus bent, they are not in 

 action, the whole fore parts being retracted by the contraction of 

 other muscles. 



Lateral longitudinal, muscles (11, 11) are inserted into the head, 

 and passing down each side are again inserted into the skin at the 

 hindmost transverse band : these retract the skin. 



Longitudinal muscles for the drawing in of the foot (12, 12). 

 They are inserted into the skin of the neck on each side, and into 

 the foot-bulb. 



Diagonal foot-muscles (13, 13) inserted into the skin at the hind- 

 most transverse band, and into the sides of the foot-bulb. Their 

 use, in conjunction with the preceding, is to draw the foot-bulb to 

 either side. 



A pair of small muscles (15, 15) are attached to the extremity of 

 the intestine (which is drawn in a dotted line) and to the skin of the 

 projecting points of the anus. These are possibly mere ligaments 

 to keep the intestine in its place, or may perhaps be merely the out- 

 line of a short rectum. 



The foot (17) is partly sheathed in the foot-bulb (16) by a folding 

 of the skin ; it is 'drawn up to either side, by either of the foot- 

 muscles (18, 18), or drawn in by both acting together. 



The conical toes, somewhat flexible at the tips (19), are capable of 

 independent action. They are separated by the contraction of a 

 pair of muscles (20, 20), the expansors of the toes, and are brought 

 together by that of the closers (21). These all have their anterior 

 extremities inserted into the foot-bulb. 



Besides these, the head-mass is attached to the skin by several 

 muscles, five or six (or even more) on each side. When the head is 

 much retracted, and the skin somewhat inverted, these muscles are 

 seen at great length, inserted at different distances from the edge. 

 Some of them are furcate, and are attached to the head-mass by two 



