ALTEENATE GENERATIONS. 241 



a community the different animals are hardly 

 larger than a good-sized pin's head ; and yet 

 every individual has a digestive cavity and a 

 complete system of circulation. 



Its body consists of a cavity enclosed in a 

 double wall, continuing along the whole length 

 of each branch till it joins the common stem 

 forming the base of the stock. In this cavity 

 the food becomes softened and liquefied by the 

 water that enters with it through the mouth, and 

 is thus transformed into a circulating fluid which 

 flows from each head to the very base of the 

 community and back again. The inner surface 

 of the digestive cavity is lined with brownish-red 

 granules, which probably aid in the process of 

 digestion ; they frequently become loosened, fall 

 into the circulating fluid, and may be seen borne 

 along the stream as it passes up and down. The 

 rosy tint of the little community is due to these 

 reddish granules. 



This crowd of beings united in a common life 

 began as one such little Hydra-like animal as I 

 have described above, floating free at first, 

 then becoming attached, and growing into a 

 populous stock by putting out buds at different 

 heights along the length of the stem. The for- 

 mation of such a bud is very simple, produced 

 by the folding outwardly of the double wall of 

 the body, appearing first as a slight projection 

 11 p 



