208 SYDNEY J. HICKSON. 



they would say the gonophore is an " individual ; " in the 

 other, it is an " organ." 



I am not inclined, however, to believe that it is possible 

 to draw a sharp distinction between these two ideas. They 

 are relative ideas, as Claus (5) maintains, just as "cell" 

 and " tissue," " individual " and " colony," must be. 



The stimulus of the sexual cells of a certain size would 

 produce the same effect if they were formed in the coenosarcal 

 canals or the zooids; but natural selection has stepped in 

 in the case of the Hydi'ocorallines, so that in the case of 

 Millepora the gonads do not produce this effect until they 

 reach the zooids, and, in the case of the Stylasteridae, not 

 until they reach certain parts of the canal system. 



The two kinds of gonophores are, then, to my ideas really 

 homologous, although in the one case they have reached such a 

 stage of development as to justify us in considering them 

 " individuals," Avhile in the other case they cannot be con- 

 sidered more than sexual " organs." 



General Conclusions. 



1. In Millepora murrayi (sp. ?) the male gonads are 

 borne by medusae which escape from the ampullae in which 

 they are developed before the spermatozoa are matured. 



2. The ova of this species are, like the ova of Millepora 

 plicata, extremely small and alecithal. They move in an 

 amceboid manner in the coenosarcal canals, and do not ulti- 

 mately rest in gonophores, nor in any specialized portion of 

 the system. 



3. The medusae of Millepora murrayi have no radial 

 nor ring canals in the endoderm of ^he umbrella, no velum, 

 no sensory organs, and no mouth. 



4. The medusae are formed by a metamorphosis of an 

 ordinary zooid ; in the majority of cases dactylozooids, but 

 in others gastrozooids. 



5. The sperm-cells originate in the ectoderm of the coeno- 



