MUSCULAR SYSTEM. 73 



the first pair, in which the muscle answering, as I suppose, 

 to (a), namely, the flexor of the upper segment of the 

 pedicel, is much spread out at its lower end, and is there 

 attached to the exterior surface of the lower segment. 



The backward and forward movements of the segments, 

 both in the rami and in the pedicels of the cirri, are appa- 

 rently effected, as already noticed, by the outer or inner (as 

 the movement may be) basal edge of one segment being 

 drawn a little way down within the next succeeding lower 

 segment. If, at the same time, both the inner and outer 

 margins of all the segments were drawn one within the 

 other, the whole limb would necessarily be shortened ; and 

 I distinctly saw a shortening action, with very slight move- 

 ment in any other direction, in the first and second pairs 

 of cirri ; and I think it almost certain that this movement 

 might be performed by the other cirri. If I correctly under- 

 stand a statement of Milne Edwards,* this is an important 

 fact, as he asserts that only the higher Crustaceans possess 

 the power of shortening their limbs. 



When a Cirripecle is alive, the action of the cirri is really 

 beautiful : from the position of the thoracic segments, the 

 posterior cirri (three pairs in the Balaninae and four pairs in, 

 the Chtharnalinse) form a sort of semicircle facing the mouth : 

 the anterior cirri stand further apart, and are opposed in 

 pairs to each other, with the first pair pointing beyond the 

 mouth. Together the cirri form a hollow cone, not circular 

 but elongated, with the mouth situated at the lower anterior 

 end. The posterior cirri are protruded, by the movement 

 of the whole thorax, curled up, close along the carinal end 

 of the orifice ; as they are protruded, they diverge, both by 

 the movement of their pedicels, and, as I believe, by the 

 separation of the thoracic segments. As the two rami of each 

 separate cirrus are uncurled, they also diverge a little ; as 

 do the double rows of spines on the segments in each 

 ramus, by their elasticity. By the movement of the thorax, 

 the cirri are then swept towards the rostrum; and, lastly, they 

 are brought perpendicularly down towards the mouth with 

 a rapid movement, which would be beautifully adapted to 

 catch any object floating or swimming in the water ; hence 



* 'Annates des Sciences Naturelles,' torn, xviii, 1S52, p. 121. 



