LIFE IN A SPONGE 319 
which are almost contiguous, and is distinguished by the 
three apical teeth of the telson. The third species, diga 
psora (Linn.), has the eyes well separated, and the inner 
branch of the uropods emarginate on the inner side near 
the apex. Because of the latter character Leach called it 
emarginata, a name that would be naturally supposed to 
apply to the telson, and which fortunately had to make 
way to an earliername. ‘The fourth species, AV/ga monoph- 
thalma, Johnston, is not very happily named, since there 
are very conspicuously two large elongate eyes, though 
they happen to meet apically. The terminal segment of 
the pleon has a central carina. It attains a length of more 
than two inches. That which Johnston supposed to be a 
variety of this species has been determined by Schiddte 
and Meinert to belong to dvga Strému. Twenty species 
in all are distinguished by those authors, who point out 
that the genera Pterélas, Guérin, and A’gacylla, Dana, are 
synonyms of Adiga. Alga crenulata, Liitken, has been re- 
corded from Scotland. The species Aga spongiophila, 
Semper, is notable for making its home in the beautiful sili- 
cious sponge, Huplectella aspergillum, of the Philippines, in 
which it can scarcely be expected to live by sucking the 
juices of fish, but it is probably well supplied with food 
from the other crustaceans and small marine animals 
of various kinds which enter the glass-rope basket by 
accident or design, and find themselves entrapped within 
it in presence of a dangerous foe. Avga Schioedteana, 
Bovallius, was described in 1885, Avga Lovén, Bovallius, 
in 1886. 
Of Rocinela Schiédte and Meinert distinguish from 
various parts of the world nine species, the type being the 
British Rocinela danmomensis, Leach. focinela signata, 
Schiddte and Meinert, is found in the West Indies and 
Central America. To one or other of these two species, 
the other seven are said by Hansen to approach very 
closely. He points out that both in Av’ga and Rocinela the 
structure of the maxillipeds is probably adapted to pulling 
apart the skin of a fish and clearing a space for the attack 
of the mandibles. He considers Alitropus foveolatus from 
