METAZOA COELENTERA. 95 



In 1886, Hickson 1 observed that the generative prod- 

 ucts of Millepora were formed in little capsules in the 

 walls of the canals and that both male and female cap- 

 sules were found in the same canals. This author has 

 also described and figured 2 the medusae of Millepora. 

 These are formed by a metamorphosis of an ordinary 

 zoon, usually a dactylozooid but sometimes a gastrozooid. 

 They occur in ampulla-like cavities of the coenosarc. 

 When they leave the parent form they are without the 

 radial or ring canals, veil (velum), and sensory organs 

 common to the more specialized medusae. It may be 

 that these develop later while the animal swims about in 

 the water, or it may be the medusae remain in a primitive 

 condition. 



PI. no, fig. i, is a section through a medusa of Mille- 

 pora murrayi. It has a well developed manubrium (the 

 part hanging down like a handle), containing a cavity 

 continuous with a large canal of the parent stock; the 

 rounded masses on either side of the manubrium repre- 

 sent the sperm, and the outer encircling portion the um- 

 brella. The ectodermal parts are shaded pink and the 

 endodermal blue. Fig. 2 is a section of an older medusa 

 that is not organically connected with the colony at any 

 point and is probably ready to escape. 



Distichopora (No. in) has a beautiful pink skeleton. 

 The openings are not in groups as in Millepora, but are 

 either in rows along the edges of the branches or arranged 

 in wavy lines over the surface. The rows of pores con- 

 sist of a middle row of gastrozooids with dactylozooids on 

 either side. The ampulla-like cavities in this genus are 

 on one or both faces of the branch. The gonophores are 

 not metamorphosed dactylozooids, becoming free-swim- 

 ming medusae, but are modifications of the ova and sperm 

 cells in the canals of the coenosarc which never become 

 detached. 



!Proc. Roy. Soc. London, XL, 1886, p. 325. 

 2 Quart. Journ. Micr. Sci., XXXII, 1891, p. 375. 



