374 NUDIBRANCHIATA ; DORIS, TRITONIA, GLAUCUS. 



having been discovered by late researches. The position of the 

 gills varies in different genera. Thus in the Doris (Fig. 568), 



FIG. 568. DORIS CORNUTA. 



FIG. 569. TRITONIJ 



they are arranged in a circular form around the termination of 

 the intestine. In the Tritonia (Fig. 569) they are placed in 



FIG. 570. THETYS LEPORINA, UPPER AND UNDER SIDE. 



tufts on each side of the back. In the Thetys (Fig. 570), also, 

 they are arranged in two rows 

 along the back ; this animal is 

 remarkable for the large mem- 

 branous fringed hood, which 

 covers the head. In the Glaucus 

 (Fig. 571) they form two or 

 three large tufts on each side, 

 which give assistance in swim- 

 ming. These beautiful little 

 Mollusks are inhabitants of the 

 Mediterranean and Indian 

 Oceans; their hues are azure blue 

 and silver ; and they swim with great rapidity on their backs. 



FIG. 571. GLAUCUS FORSTERI. 



