164 TOILERS IN THE SEA. 



reproductive function is arrested, or in abeyance, for 

 buds to be produced on different parts of the Medusa- 

 like structure, sometimes on the central canal, but 

 most commonly near the base of the tentacles, at the 

 lower margin of the swimming-bell, and the buds 

 thus produced originate free zooids, in all respects 

 like the parent from which they sprung. 



The reproductive elements are produced, in the 

 free swimming polypes, either between the two 

 membranes of the central pendulous tube, or they 

 are enclosed in special cells, or sacs, seated on the 

 radiating tubes. Sometimes they make their ap- 

 pearance before the liberation of the free zooid, and 

 sometimes not until long after the zooid becomes free, 

 the ovaries in one individual, and the spermaries in 

 another, so that, typically, the free swimming polypes 

 are either male or female. 



It must not be supposed that all the genera pro- 

 duce the free polypes, for in some groups the sexual 

 polypes always remain fixed, although this is regarded 

 as being a less highly developed form of reproduc- 

 tion, and is subject to various gradations, some being 

 simple, and others much more complex. In one 

 sub-order the reproductive buds are borne on an off- 

 shoot of the polypary, enclosed in an urn, or capsule, 

 of similar substance to the residue of the horny 

 skeleton. This is a large section, and contains some 

 of the commonest, most interesting, and best-known 



