42 HYDROIDS AND JELLY-FISHES. 



whips, and entangle in them the little shrimps, shell- 

 fish, or any other food that may fall in their way. They 

 have also to eat and digest for the whole family ; and 

 then the food, reduced to a pulp by the process of di- 

 gestion, passes through the whole community by means 

 of the stems, which, as I have told you, are hollow 

 tubes, and communicate with each other. Next, there 

 are the swimmers ; for this community is not attached, 

 but floats freely in the water : their office is to move 

 the whole establishment ; and one may see such a Hy- 

 droid community moving along like one individual, 

 though all the motion is performed by these swimming 

 members alone. Finally, there are those whose business 

 it is to produce the buds that bear the little Jelly-Fishes j 

 and so well is this wonderful community regulated, that 

 each one performs his own work faithfully, and never 

 interferes with the affairs of his neighbor. 



A pretty example of these compound households, 

 leading a common life and moving as one being, is the 

 Nanomia, which may be found upon our immediate 

 coast, in the Lynn Bay, or off the shore of Nahant. 

 On the next page is its picture (No. 33).* The oval 

 ring at the top is formed by a little oblong sac which 

 contains oil, and serves the little community as a balloon 

 or float, steadying it in the water. This float is as 

 transparent as a bubble of glass, and deep red when 

 seen in certain lights. Just below the float you see 

 a cluster of bell-shaped organs. These are the oars ; 

 by alternately opening and closing, they have the 

 power of taking in and throwing out water, and 

 thus they drive the community along. Below these 

 * Sea-Side Studies (A. Agassiz). 



