TUNICATA. 91 
Molgula giga/itea, which is one of the largest) of the Ascidians, 
and which attains a length of over thirteen inches, forms a tough 
conical sac ; the branchial and atrial orifices at the upper end 
have six and four lobes respectively. The test is leathery, smooth 
above, but coated with sand below. The exhibited specimen, 
which comes from the Straits of Magellan, has several specimens 
of the stalked Bolteuia legumen attached to the lower part of the 
test. 
The curious Molgula oculata (Fig. 10) has a soft oval or rounded 
body coated with sand. The branchial and atrial orifices have res- 
pectively six and four lobes. Specimens grow attached to the rocks 
and also live free in the sand. The surface of the test is provided 
with hairs, which adhere to the rocks and collect particles of sand. 
The adhesion not being very firm, specimens are easily detached by 
Mogula oculata. 
a, branchial ; b, atrial orifice. 
currents and collected into heaps by the eddies ; when living in the 
sand only the two dark orifices are visible. The sand coating has 
been supposed to confer protection by mimicry of the environment ; 
but Professor Lacaze Duthiers found, much to his chagrin, that 
the sandy tests of his specimens were of no avail in securing them 
from being devoured by crabs who seemed to scent their prey 
from afar. 
In the family Cgnthiidce, the test is usually leathery, the 
branchial and atrial apertures four-lobed, and the branchial sac 
folded into longitudinal pleats. 
