115 
and Functions of the Sponge. 
a fecal orifice formed exactly at the place of the junction between 
two branches of the Spongia oculata and communicating with 
both, although these branches were hanging by different stems 
and separate roots, from the roof of a small cave. When branches 
of the Spongia xerampelina or ventilabrum , or of the Spongia 
prolifera , are kept in contact with each other, by the washing up 
of stones against them by the tide, or by tying them together, 
they anastomose in the freest manner, and produce combinations 
of form, which render the distinction of branched species by 
that character extremely perplexing. This power of uniting is 
much more strikingly exemplified in the sessile species ; for we 
frequently observe the side of a rock studded over with separate 
young Spongia papillares, not larger than a pea, which, in the 
course of a few weeks, unite into a continuous surface of sponge 
of more than a foot square ; and it is amusing to observe the 
spreading and uniting of the young Spongia parasitica ?, on the 
back and legs of the living Cancer araneus, Pent., where they 
frequently collect to the number of forty or fifty, interrupt the 
joints of this lazy crab, spread like a mantle over its back, and, 
from want of space to creep upon, rise in fantastic ornaments 
upon its head, which the crab is unable to remove, from the 
small extent of motion admitted of by its hinge-like joints. 
Different species of sponge do not unite together when they 
come into contact ; they form a slight adhesion, but the line of 
separation is easily traced, and they can be disunited without la- 
ceration. When the Spongia tomentosa meets the Spongia pa- 
pillaris the margins of both adhere together, rise a little from 
the rock, and proceed directly outward, as if endeavouring to sur- 
mount each other, till their contest is arrested by the action of 
the waves, which would soon tear off the unsupported margins, 
if they proceeded outward to any considerable extent. This 
power of uniting, possessed by the individuals of the same spe- 
cies, is common to the sponge with plants ; and, as is proved by 
uterine monsters, with all the higher orders of animals, and is 
the reason why we frequently find even the small sponges of the 
Frith of Forth covering a continuous surface of several square 
feet As I have found sponges of such magnitude on various 
parts of our coast, accessible at ordinary tides, and very nume- 
"h 2 
