154 TOILERS IN THE SEA. 



matter to obtain a good view of a colony with the 

 animals extruded, as they retract themselves at the 

 slightest alarm, and, when transferred from the sea to 

 an artificial aquarium, there are few of them which 

 will thrive, or, if they continue to exist, will manifest 

 that vigour which characterises them in their native 

 element. Many efforts have 

 been made, with more or less 

 of success, to kill the animals 

 suddenly, when expanded so 

 as to mount them in fluid, as 

 permanent objects for the 

 microscope. The theory is 

 FIG, 25. OPERCOLUM OF that if fresh water can be 



SERTULARIA. 



ejected upon them, when ex- 

 truded, it kills them instantaneously, before they are 

 able to withdraw ; but it is not so easy to put the 

 theory into practice, because a very slight motion of 

 the water is sufficient to cause their withdrawal. 

 Some of our friends claim to have achieved a fair 

 amount of success, by carefully taking the living 

 animals to a short distance only, in a vessel of sea- 

 water, and then transferring them to a saucer, at the 



study of these animals, may be found in "A History of the 

 British Zoophytes," by Dr. George Johnston (1847), or in the 

 more recent " History of British Hydroid Zoophytes," by 

 Thomas Hincks. London, 1868. Both published by Van 

 Voorst. 



