134 INVERTEBRATE ANIMALS. 
outer water. They are therefore “ branchiate” Annelides. As 
they live in tubes, however, and do not voluntarily expose more 
than the anterior end of the body, the branchiz are all placed 
on or near the head. The filaments of which the gills are 
composed (fig. 60, @) are richly ciliated, and as the pseudo- 
heemal fluid is usually red, they have generally a beautiful 
scarlet colour. 
The most familiar of the Zwdzcola is the Serpula (fig. 60, a), 
the contorted and winding tubes of which must be known to 
every one as occurring on shells or stones on the sea-shore. 
One of the cephalic filaments in Serpula is much developed, 
and its extremity forms a kind of conical plug or ‘‘ operculum,” 
which serves to close the mouth of the tube when the animal is 
retracted within it. In Spzrorbds (fig. 60, 4) the shelly tube is 
coiled into a flat spiral, which is fixed to some solid object. It 
is of extremely common occurrence on the fronds of sea-weed, 
and on other submarine objects. 
OrDER IV. ErrantiA.—The Annelides comprised in this 
order are called “errant” (Lat. erro, 1 wander), or “roving,” 
Say tte aull gy: 
SY, 
— , »y 
eS gaa 50522, Ae ae eS Se 
Fig. 61.—‘‘ Errant” Annelide. Nevezs, showing the head with its appendages, 
and the bristle-bearing  foot-tubercles. 
from the fact that they all lead a free existence, and are never: 
confined in tubes. They have always lateral unjointed append- 
ages, or foot-tubercles (fig. 61), which carry tufts of bristles, 
and a soft jointed filament or cirrhus. The anterior rings ot 
the body are usually so modified as to form a sort of head, 
which is provided with eyes and with two or more feelers, 
which differ from the antennz of insects and Crustaceans in 
not being jointed. The mouth is placed on the inferior surface 
of the head, and is sometimes furnished with one or more pairs 
of horny jaws which work from side to side. The upper part 
