56 NOTES ON 
CHAPTER VII. 
ON THE GREEN AND BROWN POLYPE. 
Hydra viridis et grisea.x—Linné. 
The remarkable simplicity in the organization 
of this creature, its limited functions and sin- 
gular method of reproduction, form a striking 
contrast to the grand and beautiful machinery 
exhibited in the structure of the superior grades 
of the vertebrated animals. The perfect deve- 
lopement of their nervous system; the intri- 
cacy of construction in their apparatus for pro- 
' ducing a double circulation, for the assimilation 
of their food, and the elimination of their old 
and useless parts, are among the principal 
means by which they perform those internal 
functions of which the polype is either wholly 
destitute, or performs in the most simple man- 
ner. 
The interest attached to these creatures, from 
the station they hold among organized matter, 
apparently partaking in many respects both of 
