38 Instinct and Intelligence 



animal's body. This apparatus is described as 

 a cnidocil, and, with the palpocils, forms a 

 delicate bristle-like covering to the body and 

 tentacles of Hydra. If a small living animal 

 happens to come in -contact with these pro- 

 cesses as chemically to irritate the free ends of 

 its cnidocils, their barbed fibres are released, 

 and darting out of their cells sting the intruder 

 to death ; the prey is then seized by the Hydra's 

 tentacles, carried to its mouth, and passed into 

 its body cavity, there to be digested and 

 assimilated. 1 



Hydra fusca, like many of the Hydro- 

 medusae, is reproduced by a process of budding ; 

 but other genera of this family, such as the 

 small Obella geniculata often found attached to 

 the oar-weed, give rise by sexual processes to 

 Medusae commonly known as " jelly-fish." The 

 various phases in the reproduction of the 

 Hydroids and Medusoids, although a subject 

 of great interest is outside the province of this 

 work ; we, therefore, pass on at once to con- 

 sider the structure of a typical form of Medusa, 



1 Quarterly Journal of the Microscopic Society, February, 1905, 

 p. 615. Mr. G. Wagner on "Some Movements and Reactions of 

 Hydra.'' 



