THE GONOPHORES OF THE HYDROCORALLIN^. 207 



The original position of the gonads was the centre of the 

 concavity of the umbrella. As they became larger and larger 

 in phylogeny a conical growth of the endoderm, with respiratory 

 and nutritive functions, peneti'ated them, and became the manu- 

 brium. All of these stages may be seen repeated in the onto- 

 geny of the medusa of Millepora. When a mouth was formed 

 at the end of the manubrium the gonads were in some forms 

 (anthomedusse) restricted to the sides of that organ ;. but in 

 other forms (leptomedusse) they were shifted to a more con- 

 venient place in the radial canals. According to my view, 

 then, the manubrium of the male gonophore of Allopora does 

 not prove that it is a degenerate medusa, but, rather, that it is 

 one stage further than Distichopora on the road that all medusae 

 have travelled in the early history of their phylogeny ; that is to 

 say, a stage with a larger spermarium, and a special process of 

 endoderm for its more perfect nourishment and respiration. 



Another question arises in connection with the gonophores 

 of the Hydrocorallinse that at one time would have been con- 

 sidered one of vital importance. 



In the description given above of the development of the 

 medusa of Millepora, I have shown that it is formed by a 

 metamorphosis of a dactylozooid. This would support the 

 view, then, that the medusa is a 'modified trophosome. 



In the description of the development of the gonophores of 

 Allopora and Distichopora I do not mention the zooids at all. 

 The gonophores are not developed in these genera (figs. 12, 19) 

 in connection with either the gastrozooids or dactylozooids, they 

 arise quite independently from the coenosarcal canals. They 

 have no particular relation to the systems in which the zooids 

 are arranged, and there is every reason to suppose that they are 

 quite independent of them. Further, these gonophores are not, 

 according to my view, degenerate medusse. They must, there- 

 fore, be special organs of the colony bearing the gonads. 



To those naturalists who believe that there is a sharp dis- 

 tinction to be drawn between the idea of the " individual " 

 and the " organ " in the animal kingdom, these apparently 

 contradictory cases must be very puzzling. In the one case 



