ALTERNATE GENERATIONS. 



239 



lower end to some surface, while the inversion of 

 the upper end has formed the mouth and diges- 

 tive cavity, and the expansion of its margin has 

 made the tentacles, the very simple story of the 

 fresh-water Hydra is told. But the last page in 

 the development of these lower Radiates is but 

 the opening chapter in that of the higher ones, 

 and I will give some account of their trans- 

 formations as they have been observed in the 

 Acalephs. 



On shells and stones, on sea-weeds or on 

 floating logs, there may often be observed a 

 growth of exquisitely delicate branches, look- 

 ing at first sight more like a small bunch of 

 moss than anything else. But gather such a 



Coryne mirabilis, natural size. 



mossy tuft and place it in a glass bowl filled 

 with sea-water, and you will presently find that 

 it is full of life and activity. Every branch of 

 this miniature shrub terminates in a little club- 

 shaped head, upon which are scattered a num- 

 ber of tentacles. They are in constant motion, 



