HYDROZOAN CORALS 151 



either a testis or a simple large yolk-laden egg, or it may 

 contain a larva and a withered trophodisc. The trophodisc 

 is sometimes provided, in the male, with a central column 

 of endoderm, called the Spadix, which resembles the 

 manubrium of a medusa, and by some authors the tropho- 

 disc is regarded as a degenerate medusa. This is, however, 

 a matter that requires further investigation. 



P'lG. 70. — Distichopora. Surface view of a branch showing the ampullae. 

 ■: 2 diams. 



The ampullae can usually be seen at the surface of the 

 corallum and have the appearance of a cluster of blisters 

 each about 0-5 mm. in diameter (Fig. 70) ; and in all the 

 genera that have been examined, sexual reproduction appears 

 to be continuous, the gonophores in various stages of develop- 

 ment being found in nearly all the full-grown specimens. 

 The sexes are usually separate. Very seldom does a colony 



