THE GONOPHORES OF THE HYDEOCORALLIN^. 393 



of the Hydroidea, however simple in structure, represent 

 stages in the degeneration of medusae, may lead to the con- 

 clusion that these gonophores of the Hydrocorallines are also 

 degenerate medusse ; and it is necessary to issue a warning that 

 this is probably not the case. 



That the medusa of Milleporais not degenerate but primitive 

 in its simplicity must be apparent. 



In the course of its development there is no abbreviation nor 

 any trace of organs that were at one time functional and have 

 since become rudimentary. Moreover, it cannot be considered 

 at all probable that a free-swimming medusa, bearing immature 

 spermatozoa, would have lost its mouth, tentacles^ sensory 

 organs, endoderm canals, and velum ; or, if it is a degenerate 

 medusa, that the development of these organs would be post- 

 poned until after its escape. 



The only view that seems to me to be at all tenable is the 

 one that considers the medusa of Millepora to be primitive in 

 its simplicity. 



As regards the male gonophores of Allopora and Disticho- 

 pora, there is without doubt a close similarity in appearance 

 between certain stages in the development of the male gono- 

 phores of both these genera and the younger stages of the 

 medusae of such forms as Pennaria and other Tubularians (cf. 

 this paper, PL XXX, and Weismann (12), pi. xvii, fig. 3) ; 

 and the manubrium of Allopora is undoubtedly closely similar 

 in general appearance to the manubrium of the adelocodonic 

 gonophore of many of the Tubularise. In fact, the gono- 

 phores of some of the Hydroidea, such as Clava (Allman) 

 and Corydendrium (Weismann), are much less like adelocodonic 

 medusae, even when they reach their full development, than are 

 these gonophores of Allopora and Distichopora. 



If it could be shown that the inner membrane covering the 

 spermarium is derived from the ectoderm and is not endo- 

 dermic as I have described it, and that structures correspond- 

 ing to the '' glockenkern " do occur in the development of 

 these gonophores, then my principal objections to the view 

 that they are degenerate medusae fall to the ground. A very 



