200 SYDNEY J. HICKSON. - 



convinces me that there is in these forms no true "glockenkern," 

 and that the two membranes covering the gonad are truly homo- 

 logous 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 Stylasteridae 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 scyphis- 

 toma 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 

 Tubulariae and Campanulariae may best be conceived by sup- 

 posing 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 primi- 

 tive capacity of becoming detached, and subsequently developed 

 generative organs, while the ordinary buds lost their generative 

 function." 



Weismann's view is similar to that of Balfour. He says, 

 "Die uiedrigste d. h. einfachste Form der heute lebenden 



