THE GONOPHOEES OF THE HTDROCORALLIN^. 397 



ancestral type of Hydromedusan. The parasitic or semi- 

 parasitic habits of the actinula of most of the Narcomedusse 

 suggest that it is an extremely modified form, and it seems to 

 me to be extremely hazardous on the part of Brooks to base 

 his phylogenetic considerations upon such a weak and slender 

 foundation. The views of the earlier writers that the sessile 

 form is the more primitive, that in those cases in which the 

 medusa develops directly from the egg the trophosome has 

 disappeared from the developmental cycle, seem to be more 

 probable. 



It is not necessary to enter further into the discussion of 

 these extreme speculative questions. 



I have referred to them not in the hope of adding anything 

 new, nor of throwing light upon them, but in order that I may 

 place clearly before the reader the position I take with regard 

 to them. 



It seems to me to be more satisfactory to regard the sessile 

 trophosome rather than the free-swimming actinula as the 

 primitive type, and the medusa as a structure produced 

 originally by a polypoid colony for the nourishment and dis- 

 tribution of the gonads. 



Having thus stated my opinion as to the original form of 

 Hydroid, it is necessary to go further and express an opinion 

 as to the mode in which medusae originated. 



The views of Weismann and Balfour on this question are as 

 nearly as possible identical. They supposed that the medusa 

 originated by certain buds bearing the primitive sexual cells, 

 retaining their primitive capacity of being detached from the 

 parent, and that such buds became modified for a free-swimming 

 existence. According to these views the medusa is homologous 

 with a polype, it is simply a modified trophosome, or that 

 trophosomes and gonophores are both modifications of some 

 common type. 



Huxley's original view that the gonophore is a peculiar 

 sexual organ has in recent years been subject to a storm of 

 criticism, and there are very few naturalists of the present day 

 who would defend the position he took. " A raedusoid, though 



