402 SYDNEY J. HICKSON. 



medusae. They must, therefore, be special organs of the 

 colony bearing the gonads. 



To those naturalists who believe that there is a sharp dis- 

 tinction to be drawn between the idea of the " individual " 

 and the "organ" in the animal kingdom, these apparently 

 contradictory cases must be very puzzling. In the one case 

 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 eflFect if they were formed in the ccenosarcal 

 canals or the zooids; but natural selection has stepped in 

 in the case of the Hydrocorallines, 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 Stylasteridee, 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," while 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 

 amoeboid manner in the ccenosarcal 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 cndoderm of the umbrella, no velum, no 

 sensory organs, and no mouth. 



