ASCIDIAN MOLLUSKS. S13 
organically possessing a compound life. Through 
these last-named the transition is easy and natural 
to the lowest forms of animal life, the Polypes ; for 
the Class of animals denominated  Lryozoa or 
Polyzoa, which form the exquisite aggregations of 
calcareous cells known as Sea-mats (/lustra), and 
their allies, are truly Ascidians in their structure, 
with their entering orifice surrounded by a radiated 
circle of ciliated tentacles. 
FAMILY ASCIDIADA. 
Whoever has turned over stones at the extreme 
verge of low-water (and there is no student of 
marine natural history who has not) is familiar 
with uncouth pellucid bodies adhering to their 
under surfaces, that resemble bags, of a substance 
somewhat between leather and jelly. The dredger, 
however, is far more familiar with them, for 
scarcely can any part of the bottom of the sea be 
raked without an abundance of these curious crea- 
tures being brought up, varying much in size and 
colour. Some are sufficiently rude and uncouth, 
coarse and rough in texture, and dingy in hue; 
others are attractive, often of brilliant colours, of a 
semi-transparent clearness, resembling strange pel- 
lucid fruits, or masses of ice. They are always 
found adherent, either by the base of the sac or by 
its side, to foreign bodies, as stones, shells, and 
sea-weeds, and thus not only are they deprived of 
locomotion, but almost of all appearance of vitality, 
for no movement is perceptible in them externally, 
except the periodical opening and closing of the 
two orifices which give admission and exit to the 
currents of water for respiration and food. 
