THE MEDUSA OP MILLEPORA MUEEAYI. 



381 



microscope, the arrangement of the zooids, medusje, and 

 coenosarcal canals can be very readily observed. The figure I 

 have given was drawn, by the help of the camera, from such a 

 preparation. The larger canals to which I have referred above 

 form a wide-meshed network immediately below the surface. 

 Each mesh is an irregular polygonal figure embracing the 



Woodcut 1. — Diagram of the arrangement of the zooids and medusae of 

 Millepora murrayi. G. Gastrozooids. D. Dactylozooids, M. Me- 

 dusae. The larger canals are represented by irregular black lines. 



whole of one circular system of zooids. The medusse are 

 always found either upon or quite close to these large canals, 

 and thus they are sometimes without the circles, and some- 

 times in a position corresponding to that of a dactylozooid of 

 the regular circle. 



The position of the medusae in the colony cannot be used as 

 an argument against my statement of their origin ; in fact, 

 whatever bearing it may have is in its favour. 



4. When a decalcified specimen of Millepora is examined 

 from above, a cluster of large nematocysts may be seen at the 

 mouths of the gastropores and dactylopores. They may also 

 be seen in sections (figs. 1, 2, 6, 7, Nemat.) . When the medusa 

 is formed and the pore closed by the operculum these large 

 nematocysts can be of little or no service, so they arc shot 

 and no new ones take their place. In the figures of the 

 sections through the older medusae (9, 10, 11) the reader will 

 notice that none of these large nematocysts are to be seen. 

 Where the operculum is not completely formed (fig. 8), 



