394 SYDNEY J. HICKSON. 



careful examination of my sections of gonophores in all stages 

 of development convinces me that there is in these forms no 

 true " glockenkern/' and that the two membranes covering 

 the gonad are truly homologous with the two membranes 

 covering the ova, namely, an outer ectodermic membrane and 

 an inner endodermic membrane. 



The manubrium of the gonophore of Allopora is, I believe, 

 strictly homologous with the manubrium of the medusa of 

 Millepora ; that is to say, it is a subsequent endodermal in- 

 growth into the spermarium developed for the purpose of 

 affording increased nourishment to the rapidly increasing sper- 

 moblasts. 



These gonophores, then, do not represent, in my opinion, 

 stages in the degeneration of medusae. The Stylasteridse never 

 possessed free-swimming medusae, I believe, although their 

 gonophores may indicate to us some of the stages that the 

 medusae of Hydroidea passed through in the course of their 

 phylogeny. 



Before entering into a discussion of the meaning of the 

 gonophores of the Hydrocorallines, it is necessary to consider 

 briefly the principal views that have been put forward con- 

 cerning the primitive or ancestral form of the Hydrozoan. Is 

 it probable from the evidence at our command that the ances- 

 tral form was a fixed colonial hydroid, or was it like a 

 scyphistoma larva (Hydra tuba) ; or, lastly, was it a floating 

 Hydra or actinula ? 



Balfour says, " A condition like that of Hydra, in which the 

 ovum directly gives rise to a form like its parent, is no doubt 

 the primitive one, though it is not so certain that Hydra 

 itself is a primitive form. The relation of Hydra to the 

 Tubularise and Campanularise may best be conceived by 

 supposing that in Hydra most ordinary buds did not become 

 detached, so that a compound Hydra became formed ; but that 

 at certain periods particular buds retained their primitive 

 capacity of becoming detached, and subsequently developed 

 generative organs, while the ordinary buds lost their gene- 

 rative function. ^^ 



