AND HABITS OF THE AMMOCHARIDA. 243 
motion. It is beg manipulated by the “ Lippen-organ” (J.0., 
Pl. 23. figs. 1 & 3, Pl. 24. fig. 7) which, protracted and retracted 
at each movement, is apparently licking or rasping it, as would 
the radula of a mollusk. After a few minutes’ treatment, the 
fragment may be ejected by the “ Lippen-organ,” which, pro- 
truding between the lobes, thrusts it upwards, within reach of 
the ejecting tentacles, which complete the expulsion from the 
crown. One cannot doubt that, although these worms also 
swallow fine grains of sand, the process just described is an act 
of feeding. We may assume that the material last secured, 
although bearmg food upon its surface, was unsuitable for 
building purposes; but when, by chance, a tempting flat grain 
of sand, or preferably a minute fragment of shell, is obtained, 
the “ Lippen-organ ” assumes a different réle, namely that of a 
builder; a function the probability of which was suggested by 
Gilson (27. p. 381).* The selected fragment is then passed 
down into the vestibule as before, and there subjected to the 
treatment just described, but for a much longer period. By 
this process any available nourishment is doubtless at once 
removed from the surface, and the material is most carefully 
cleaned. Then, all being ready, the “ Lippen-organ ” (J.0., Pl. 23. 
fig. 1), having turned the fragment into such a position that the 
thin edge is uppermost, begins to rise steadily, carrying the 
fragment in front of it. The two lateral branchial lobes separate 
themselves widely apart to allow of the passage, and the margin 
of the crown, between the ventral branchiz, becomes simul- 
taneously stretched. 
The upper surface of the “ Lippen-organ,” with its two bilobed 
ends, is now visible, carrying the shell, which it intends to fix to 
the outer side of the tube. In another moment, the position of 
the fragment is so changed that the flat side, instead of the 
edge, shall rest upon the “ Lippen-organ ”; and this centinues 
to rise, until its bilobed extremity is made to project between 
the lateral ventral tentacles, and to touch the exterior base of the 
elastic conical tip, which, by retraction of the cephalic segment, 
* In this connection it is curious to note that, at times, the worm appears 
greatly to prefer building with white materials, and even specimens from 
Naples (where, to judge by their tubes, only black materials are available) have 
been noticed to select white when they had the opportunity, and to reject 
darker ones supplied to them. What means of colour perception such an 
organism can possess is an interesting question. 
17* 
