ECHINODERMATA OF NEW ENGLAND. 11 



with life. The time of day seems not to matter but the tide 

 is a ureal factor. At low tide we expect littoral, at high tide 

 pelagic animals. At night conditions are favorable at about 

 half-past eight when the sea appears calm. Calm weather 

 is a desideratum, and a glassy calm is a very favorable op- 

 portunity. 



In night-fishing an incandescent electric light may be 

 hung at the mouth of the net to attract animals. The color 

 of the phosphorescence corresponding to different animals 

 must be learned by experience. 



III. CGELENTERATA. 



The animals of this group have a great variety of ex- 

 ternal outlines, but several common anatomical likenesses. 

 In their simplest form the bodies consist of a simple gelat- 

 inous bag, fixed to the ground or free-swimming. There 

 is an opening called the mouth at one pole, while the whole 

 cavity of the sac serves as a stomach or is in free commu- 

 nication with the exterior medium through the mouth-open- 

 ing. In most of these animals the body cavity is continu- 

 ous with the stomach. In many there is no body cavity 

 except the stomach, a characteristic which has given the 

 name of Ccelenterata to the group. 



Rising higher than the simple sac, whose walls serve 

 as the linings of a stomach and whose opening is a mouth, 

 we pass to those where thread-like organs called tentacles, 

 which serve to capture food, are placed in a ring about the 

 mouth, and higher still to those where portions of the body 

 walls are inflated into a bell-like structure for locomotion. 

 Here we find added also sense capsules and complicated 

 sucker-like oral appendages, the modifications in which 

 will be more minutely described in considering the differ- 

 ent genera. These organs generally take a radial arrange- 



