INTRODUCTION. 
XV 
ei *closed in horny or calcareous cases, yet they 
? 0 not grow indiscriminately in any situation, 
^t exercise a faculty of selection. This is very 
•ffercnt from the selection of soils by plants, 
'hich imbibe their nourishment through their 
t J°ts ; for though rooted, all nourishment in 
hese creatures is taken through the polype 
°uths. Among the Hydroida the Sea Beard, 
[futennularia antennina ) prefers oysters and 
her bivalves, but is also found on stones and 
t aQ d ; the form of the whole varying according 
p the locality. The Sea Oak, ( Sertularia 
t prefers the fronds of fuci growing near 
, e tide marks, or the declivities of rocks in 
altered situations; the Sea Threads, the fronds 
^ the larger fuci and the margins of pools, 
ht they have been found abundantly on the 
a s of a shark ; the Sea Bristles, dead muscle 
..^ls and horny corallines. This is the case 
till? ^ ie Sea Anemonies, but as they are 
j^od and locomotive it is not so much a 
] 0 att er of surprise. Some species prefer one 
f (| C . ‘ty, and others another ; some the smaller 
Sq C] * and others the larger; but the situations 
Hi fitimes selected are exceedingly curious; 
* the small climbing Coralline ( Campanularia 
0 f u ° u tis,) has a prediliction for the antennae 
1 0 Cr abs, where it can enjoy the advantages of 
in nofnliimi itc nrou 
Ui 
^oiotion in catching its prey. 
A his power of selection is also to be found in 
]) r Ascidian Zoophytes; thus the Flustra lineata 
t|, e e *' s flat stones between tide marks, while 
| ( , C| ™ cmbranipora Peachii most commonly se- 
<u s . a dead muscle valve and sometimes the 
C °y ster and great Pinna; the purple Tubuli- 
5$ e a / Serpens) prefers corallines, while the 
t| le f a t ( Fluslra membranacea) always encrusts 
l0u d of the great sea weed ( Laminaria digi- 
