1887.] 



ON C YCLE STHERI A HISLOPI. 



35 



of the trunk, rendered possible by the several segments being 

 to a certain extent movably articulated together, admit, as 

 above stated. of a creeping or burrowing locomotion when the 

 animal is on the bottom. Very often, however, no appreciable 

 locomotion is thereby effected, and in such cases the move- 

 ments are much slower, being made exclusively to cleanse the 

 branchial feet from foreign matter, or, when the animal lies bnried 

 within the mud, to throw away the mud from the inferior edges 

 of the snell, in order that the play of the branchial feet may 

 go on without trouble. 



Movements of the Tall The tail admits of being moved but 

 very slightly on the last segment of the trunk, and this move- 

 ment is in most cases well-nigh imperceptible. On closer exami- 

 n at ion, however, the anterior part of its dorsal edge is sometimes 

 found to jut out, as it were, within the adjoining part of the last 

 segment of the trunk, and. at other times, a similar appearauce 

 may be observed at the opposite side ventrally. This must 

 indicate the existence of a very slight flexion and extension 

 on the last segment of the trunk, effected by the aid of the 

 ventral and dorsal muscles joining this part anteriorly. 



Movements of the Et/e. — These movements are very slight 

 and easily overlooked. On closer examination, however, a peculiar 

 trembling of the eye may at times be plainly seen, caused 

 by a very faint rotation of the eye-ball within its hollow. This 

 rotatory movement is effected by the alternating contraction 

 of the three above-mentioned muscles converging on either side 

 to a point at a short distance from the eye, and having their 

 insertion on the hyaline capsule investing that organ. The ocellus, 

 on the other hand, is always quite immobile. 



Movements of the Antennalæ. — The antennulæ, which gener- 

 ally hang straight down from the head, also admit of being swung 

 to a certain extent, so as at times to point obliquely forward, 

 at times backwards, their tip being in the latter case brought in 

 close approximation to the oral parts (see Pl. VIII, fig. 1). In 

 no case, however, can these organs be projected beyond the edges 



3* 



