UKNATELLA GRACILIS, A FRESH-WATER FOLVZOAN. 
7 
terminal bell. Frequently also in like manner the primary brandies give oft s(‘condary 
ones. See figures of Plats I, and also the accompanying woodcuts. 
1. Young Urnatella, in which one stem con- 
sists of a simple pedicel with a polyp-bell, 
and the other stem is divided into two seg- 
ments besides the polyp-bell. 
\ ' 
'\ - 
u 
\ 
^ 
2. Young Urnatella, in which one stem 
consists of two segments supimrting 
the polyp-bell, and the other of three 
segments with the polyp-bell. The 
first segment of each stem has as- 
sumed the uni-like form. 
llarely, a branch, consisting of two or more segments, is given off, apparently witli 
no regularity, from any other of the segments of the main stem tlian the usual ones, 
as represented in figure 4, Plate T. 
Sometimes the polyp-stock of UniateUa consists of a single stem arising from its 
hast', and at others it may consist of a number up to half a dozen, starting from the 
same disk of attachment. , 
The stems of Urnatella are highly flexible, but not contractile or capable of lieing 
visibly shortened or narrowed, except perhaps in the case of the one or two segments 
next the bell, which sometimes appear feebly contractile, especially in young s,H-«-imens. 
In the usual condition the stems appear nearly straight, or slightly curxed, but after 
intervals of ciuiescence they are observed spontaneously and rather abruptly to bi-nd 
and twist, as if wearied from remaining so long in the same position. Not unfre- 
quentlv the movement is quickly repeated before the polyps resume thmr tcm,H,rary 
rest. Similar movements arc to be seen in the con.pnttively loi.R nn«.Bn,ento.l 
petlioels of the .narine MiceHma. In UnmtM., the movement evteinis thro,.«ho..t 
Ihe entire length of the segmentetl stem, and is by no means conhned to tl.c 
terminal more flex, bio segn.cnts. ns n.igl.t be sn,, posed from „ view ol ‘ * 
of Like the latter, Cemt* is exceedingly senstt.ve ; w.th > 'b 
distnrbanec the tenta.les are qniekly .lonbled on themselves and . 
mouth of the bell, which is then closed by contraction, and the »t, ,s s.ul, . nly 
bowed outwardly, so that the heiul is brought to the ground, or when the stem long. 
