SQUIRTS, POLYPS, AND JELLY-FISHES. Q\ 



all the animals of the class we are now considering 

 the extremities of the tentacles are provided with 

 peculiar ' nettle-cells,' which by a special arrange- 

 ment can discharge from their interiors small barbed 

 bodies or styles useful as weapons of both offence 

 and defence. In Pennaria nettle-cells similar to 

 those of the tentacles are also contained in the 

 axis of the body, but what their function is in 

 this position remains untold. 



Many of the wrecks that appear on our coast 

 bring to us bunches of slender hollow tubes, meas- 

 uring as much as three or four inches in height, in 

 each of which lived at one time a delicate polyp. 

 Possibly your cluster is still alive, in which case 

 many of the tiny creatures will be seen expanded 

 at the summits of the tubes, their double circle of 

 tentacles spread out in the form of a double coronet 

 (PI. 4, Fig. 13). Hanging from some of these, 

 like bunches of grapes, are the reproductive buds, 

 which ultimately detach themselves and, medusa- 

 like, swim about in the open sea. It is not gener- 

 ally known that a large number of ordinary jelly- 

 pads or jelly-fishes, whose graceful movements on 

 the oceanic surface have from time immemorial 

 challenged the admiration of the intelligent ob- 

 server, are the products of tiny fixed colonies such 

 as we have been considering. The discovery of 

 this fact — of the dual existence led by these lower 

 organisms — is one of the most surprising in the 

 entire range of zoological investigation, and one 

 that cannot but carry with it an impressive lesson 

 of the wonderful resources of the world of nature. 



6 



