12 
black sponges, as a probable case of protective resemblance. One 
might perhaps mention in this connection the Pyura prepucialis 
(Hell.), which grows on rocks between tide marks at the coasts of 
N. S. Wales. It is found in groups on the upper side of the rocks, 
in places exposed to the surf, and is covered with a growth of fine 
algæ and the like, and looks like old, mossgrown tree stumps, or 
like irregular prominences of the rock itself. Another form grow- 
ing on the rocks at Taboga, Panama, (probably Pyura chilensis 
Mol.) is so entirely covered with algæ and sponges that it is very 
hard to distinguish it from the general surface of the rock. These 
would seem to be very fine examples of protective resemblance ; 
still I doubt very much they really could be, 11:48 hard to con: 
ceive against which enemy the protection should be meant. The 
thick, exceedingly tough mantle would seem to be protection enough; 
and against its worst enemy, man, neither the mantle nor the re- 
semblance to a piece of rock affords any protection. (The Pyura 
prepucialis is used a good deal as bait, and the Pyura chilensis 
is used as food). ; 
Hartmeyer is inclined to regard the red or yellow coloration 
of some Didemnids as a warning coloration. If it be so, then pro- 
bably also the black color of Phallusia nigra Sav."), a very con- 
spicuous form occuring f. i. on the Mangrove roots in the West 
Indies, should be regarded as a case of warning coloration, and 
perhaps the same would hold good for another Ascidian of a con- 
spicuous blue colour, found on the rocks in the bay of Panama. 
But, apart from the adventitious protection of the forms covering 
themselves with shell fragments or sand, I am not inclined to 
regard any of the instances quoted as being real cases of protect- 
ive adaptation. 
IV. Crustaceéa, 
Some of the finest instances of adventitious protection known 
are afforded by the Crustaceans, viz. the crabs which, like Steno- 
rhynchus, Inachus, Mithrax a. 0., attach algæ, sponges or the 
like to their body and limbs. — Without entering upon this well- 
known type of protection, of which I have, of course, observed 
numerous instances, I would only point out another similar case, 
") I am indebted to Dr. Hartmeyer for these Tunicate names. 
