268 "RESPIRATORY ORGANS OF AQUATIC ANIMALS. 
around the head alone, and spread out widely into the sem- 
blance of a flower. In the Nereis (fig. 52) and its allies, they 
are set upon nearly every 
division of the body, and are 
4 much smaller. Their usual 
/ arrangement in these marine 
worms may be seen in fig. 
146, which represents one 
of the appendages of Hunice, 
The tuft of gills is shown 
at 6; at ¢is seen a bristle- 
shaped filament, which may 
perhaps be regarded as the 
rudiment of a leg; and the 
projections to which the 
letters ¢ and ci point, also 
seem connected with the 
movements of the animal. 
In the Arenicola (the lob- 
Fig. 145. worm of fishermen) we find 
GrIut-turts oF SERPULA. the respiratory tufts dis- 
posed on certain segments 
only, and possessing more of an arborescent (tree- 
like) form (fig. 147). 
N\A i 
315. A somewhat similar 
arrangement is seen in the 
larvee of many aquatic In- 
SECTS, which breathe by 
means of gills ; although all 
in the manner to be pre- 
sently described. In fig. 
148 is represented the larva 
of the Hphemera (Day-fly), 
which breathes by means 
of a series of gill-tufts disposed along the abdomen, 
Fig. 146, 
GILt-TUrT or Eunice. 
perfect Insects breathe air _ 
Fig. 147. 
ARENICOLA, 
and also prolonged as a tail. In the Crustacna, we usually 
find the gills presenting the form of flattened leaves or plates. 
In the lower tribes of the class, they project from the surface 
of the body; but in the higher, they are inclosed within 
a cavity, through which a stream of water is made con- 
