5 68 
SEMIVER TERRA TES. 
1 
the vessels in the tunic. Among the five genera constituting the family, the 
typical Botryllus (figured on p. 572) has the colony thin and incrusting, with the 
individuals arranged in a circular manner, whereas in 
Botrylloides they form ellipses or branching lines. In the 
figured species of the latter ( B. albicans), from North- 
^l|j| i Western Europe and the Mediterranean, the colony is 
pure white in colour, but in some it is purple with yellow 
or green markings, and in others yellowish green. As 
an example of forms in which the colony is thick and 
massive, we may cite the genus Polycyclus. Passing over 
the second family of the suborder, we come to the third 
(Polyclinidcc), in which the colony is usually massive, 
being sometimes incrusting, but in other cases lobed, or 
even stalked. The arrangement of the individuals is 
highly variable; and the common apertures of discharge 
are usually inconspicuous. Although of an elongated 
form, the individuals usually differ from those of the 
family last noticed by being divided into three regions; 
the inlialent aperture having six or eight lobes, while the 
exhalent is frequently provided with a tongue-like process. 
The gelatinous or cartilaginous outer tunic is frequently 
stiffened by embedded grains of sand; and the branchial 
chamber is usually small and poorly developed, with 
minute gill-slits and no internal longitudinal bars. The 
tentacles are small and not numerous; the digestive tract 
is extended posteriorly to a considerable distance beyond 
the extremity of the branchial chamber; and budding takes 
place from the end of the postabdominal region. The family is represented by well 
nigh a score of genera, among which Amarucium may be selected as an example, 
on account of its numerous species. Here the colony is massive, being sometimes 
lobed or stalked; the mode of arrange¬ 
ment is usually compound and irregular; 
and the individuals are elongated, with 
six lobes to the inlialent orifice, and the 
postabdominal region elongated. The 
species here figured (A. densum) is .from 
North-Western Europe, and is character¬ 
ised by its greyish yellow colour, and 
the abundance of sand in the tunic; but 
other kinds may be black, orange, or 
rosy red, or white. In our figure, a shows 
fully active individuals; while those in 
the outer ring indicated by b assume a kind of torpid condition during the winter, 
but give rise to fresh buds in the spring. 
Omitting mention of the remaining families of the group just considered, we 
come to the third and last suborder of the typical ascidians, namely, the plios- 
AN INCRUSTING ASCIDIAN 
( Botrylloides) on a sea¬ 
weed (nat. size). 
a compound ascidian (Amarucium) in winter 
condition (nat. size). 
