CRISTATELLA. 91 



The true figure of the Cristatella is partly dependent on its age and 

 dimensions, that is, the sides are bounded by parallel lines if long, or the 

 whole is oval if short ; the extremities being always curved : according to 

 the length of the specimen the linear shape is more evident. When oval 

 its general aspect bears much resemblance to the Doris, its sole being 

 alike soft and smooth. A specimen, two inches long, is of unwieldy size, 

 and of rare occurrence in this country : nor does the breadth augment 

 in any proportion with the length. Some have much the figure of a lon- 

 gitudinal section of an ellipsoid, being convex above, flattened below, and 

 with curved extremities.— Plate XXVIII. figs. 3, 4, 5. Some are beauti- 

 fully symmetrical, as the adult, prolific subject, fig. 3, enlarged, as fig. 5, 

 the nascent specimen, Plate XXVII. fig. 13, Others, less regular, especi- 

 ally in their earlier stages, cannot be referred to any definite form* 



When a specimen is withdrawn from its native waters the whole 

 hydra? are generally replete with dark muddy matter, clearly exposing the 

 shape of the stomach. Perhaps their sustenance may be thence elimi- 

 nated ; and it is to be observed, that whenever the element they inhabit 

 becomes turbid, by the dispersion of mud among it, they are ready to 

 avail themselves of its presence. 



Nothing indicates that these creatures are carnivorous. I have not 

 observed any animalcula absorbed by them ; nor is it evident that any 

 current which the Cristatella can produce is strong enough to overcome 

 the resistance such living beings might offer against its influence. 



Though having little reason to ascribe the voracity demonstrated by 

 the hydra proper to ascidian hydrse, I endeavoured to feed those of the 

 Cristatella with the soft whitish substance of certain larvae dwelling in 

 their own element. At first they seemed to avoid it, but on repeating 

 the experiment afterwards it was surely absorbed. Yet it might not be 



* The general appearance of this creature may be explained by a homely comparison. 

 Suppose it represented in quiesence by a green satin pincushion, half the length of a lady's 

 little finger, having a flattened sole, with a border of three rows of pins, on the surface, 

 sunk over the heads. Now, the whole is smooth, but, when active, all the pins representing 

 the hydra?, rise the twelfth of an inch. Each head, with 1 00 feelers, resembles a horse shoe ; 

 and the pincushion can move along on its flat sole. 



