268 



RESPIRATORY ORGANS OP AQUATIC ANIMALS. 



around the head alone, and spread out widely into the sem- 

 blance of a flower. In the Nerds (fig. 52) and its allies, they 

 are set upon nearly every 

 division of the body, and are 

 much smaller. Their usual 

 arrangement in these marine 

 worms may be seen in fig. 

 146, which represents one 

 of the appendages of Eunice. 

 The tuft of gills is shown 

 at b ; at c is seen a bristle- 

 shaped filament, which may 

 perhaps be regarded as the 

 rudiment of a leg ; and the 

 projections to which the 

 letters t and ci point, also 

 seem connected with the 

 movements of the animal. 

 In the Arenicola (the lob- 

 worm of fishermen) we find 

 the respiratory tufts dis- 

 posed on certain segments 



only, and possessing more of an arborescent (tree- 

 like) form (fig. 147). 



315. A somewhat similar 

 arrangement is seen in the 

 larvae of many aquatic IN- 

 SECTS, which breathe by 

 means of gills ; although all 

 perfect Insects breathe air 

 in the manner to be pre- 

 sently described. In fig. 

 148 is represented the larva 

 of the Ephemera (Day-fly), 

 which breathes by means 



of a series of gill-tufts disposed along the abdomen, 

 and also prolonged as a tail. In the CRUSTACEA, 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 cavicy, through which a stream of water is made con- 



. 145. 

 GILL-TUFTS OF SERPULA. 



Fig. 146. 

 GILL-TUFT OF EUNICE. 



Fig. 147. 

 ARENICOLA. 



