ALTERNATE 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 
ll P 
