BIOLOGY. 
Ech. 19 
the urchin, generally found at the rim of the excavation, takes no part in 
the formation of the recess, though its presence may be necessary to the 
urchin. Sea-urchins appear to play some part in the formation of the 
pot-holes with a central style in which they are found at Biarritz, France, 
though they are assisted by the movements of stones under the action of 
tides and waves. 
According to Keyes (1), the study of the Actinocrinidce (for example, 
Batocrinus , JDorycrinus , and Dichocrinus) shows that at times in the 
phylogenetic history of a group variations appear to go on with broad 
and rapid strides, and the organisms survive through rapidly changing 
physical conditions. When the changes of environment became too 
rapid, the forms either ceased to exist or retrograded, and became 
depauperate and extinct. Actinocrinus and others show that variation 
ftiay go on in one part without affecting another. The Actinocrinidce show 
a tendency during their existence to increase the distal extent of the 
rays by branching, by lateral expansion of the arms, or by radial exten- 
sion of the calyx radials. 
Keyes (2) describes the relations between Calyptrceidce and Crinoids. 
KinpowitscH describes a Cirripede parasitic in the body cavity of 
Solaster and Echinaster , 
Prouho (1) finds the function of the gemmiform pedicillarise of 
urchins is to repel the attacks of starfish. When a Strongylocent?'otus 
lividus is attacked by an Asterias glacialis , as soon as it feels the contact 
of the tube feet of the starfish the little spines round the part attacked 
lie down flat, thus unmasking the gemmiform pedicillarise, which are seen 
with their jaws widely open. The moment a tube foot touches one of 
them it is bitten, and the bite seems to cause the starfish sharp pain, since 
it at once withdraws. The head of the pedicillaria remains attached to 
the bitten tube foot ; hence, after a time the urchins are unable to keep 
off the starfish, if the latter continue to attack them. If the urchin is 
pricked with a needle, or otherwise irritated, the movements of the spines 
are quite different from those performed when attacked by a starfish. 
In the first case they are all inclined towards the point of attack. 
Prouiio (2) describes a number of experiments, proving that starfish 
(Asterias glacialis) in seeking their prey are not guided at all by sight, 
but by the sense of smell, localized in the non-locomotory tube feet which 
are situated behind the ocular plate. 
Sturtz believes that no palaeozoic Ophiuroid can be referred to any 
recent form inhabiting the shore, and that all palaeozoic forms inhabited 
either deep sea or moderate depths. His investigations give no support 
to the view that the littoral fauna is older than that of the deep sea. 
Yceltzkow describes a parasitic bivalve occurring in a species of 
Synapta. It lives in the oesophagus, and is visible externally as a 
whitish grey body, which moves without changing its place. The young 
animals enter their host by the mouth. In addition a parasitic snail 
occurs in the Synapta , both fixed to the wall of the stomach and creeping 
about on the exterior. 
