604 



THE DORIS, THE EOLIS, AND THE HYALEA. 



that the back eddies of " lashers" are favorite haunts of various Water 



Suails. 



We now arrive at a very remarkable series of molluscs, which have 

 been separated by systematic naturalists into a distinct section appro- 

 priately called Nudibranchidse, or Naked-gilled Molluscs, because their 

 gills are always external and placed on the 

 back or sides of the animals. 



The common Doris is a native of our 

 own shores. All the members of the family 

 to which this creature belongs may be known 

 by the plume-like gills set in a circle on the 

 middle of the back, like the feathery coronet 

 with which the Blackfoot Indian adorns the 

 head of his horse, and the two tentacles placed 

 more toward the front. In the skin are im- 

 bedded a vast number of little spiculse. 

 The beautiful Eolis is common ou our own 



\l ,| coasts, and may be seen moving over the plants 

 'I and stones with tolerable activity and always 

 keeping the tentacles and papillae in motion, 

 sometimes contracting and sometimes extend- 

 ing them, while the movement of the water 

 The Shell of Water causes them to wave in a very graceful man- 

 Snail (Lu/maasia^ua/<6-). ner. These papillse possess the property of 

 discharging a milky kind of fluid when the 

 animal is irritated. The fluid, however, is quite harmless — at all events, 

 to the humau skin. As in the previous case, the papillse are liable to 

 fall off at a touch. 



A small but important group of molluscs now comes before us. This 

 is the Pteropoda, or Wing-footed Molluscs, so called from the fin-like 

 lobes that project from the sides, and are evidently analogous to the 

 similar organs in some of the sea-snails. These appendages are used 

 almost like wings, the creature flapping its way vigorously through the 

 water, jii.st as a butterfly urges its devious course through the air. They 

 are found in the hotter seas, swimming boldly in vast multitudes amid 

 the wide waters, and one species {Clioborealis) has long been celebrated 

 as furnishing the huge Greenland whale with the greater part of its 

 subsistence. 



The Hyalea is remarkable not only for the two wide fins which are 

 found in all the family to which it belongs, but for the long appendages 

 which pass through certain apertures in the shell and trail behind as 

 the creature proceeds on its course. The wings are united by a nearly 

 semicircular lobe. 



The Cleodora is a very beautiful and interesting animal, of which 



