144 SYDNEY J. HICKSON, M.A., D.SC, F.B.S., F.Z.S. 



of these medusae in ampullae of exactly the same size. The medusae of 

 these two forms are quite indistinguishable one from another. It seems 

 probable, then, that the Millepores from Zamboanga (Quelch), Jamaica, 

 and several othei's from unknown localities in which ampullae of this 

 character have been described bore in the living state medusae. No 

 gaps similar to these can be seen in any of the preserved specimens 

 which have been examined except those which contain or have contained 

 medusae. The fact that the largest ampullae of all specimens are of 

 approximately the same size, coupled with the fact that the medusae of 

 such different forms as those given me by Mr. Gardiner and Prof. 

 Haddon are exactly similar, suggests that the medusae of all Millepores 

 are similar. At any rate, there is no evidence at present that there is 

 any difference between the medusae of the different forms. 



It is a very extraordinary fact that the ampullae are so rarely found 

 1 have had the opportunity of examining carefully a very large collection 

 of Millepores collected in the West Indies, and deposited in the 

 Liverpool Museum. I failed to find a single ampulla in any one of 

 them, but a small skeleton sent to me by Mr. Duerden from Jamaica 

 exhibited an immense number of them. In the large collection at the 

 British Museum only a few specimens exhibit ampullae. 



It seems to be certain, then, that the medusas are but rarely 

 formed, but when they are they are formed in very great numbers. 



General Considerations. — It appears to me that these investigations 

 present very strong reasons for believing that there is only one species 

 of Mdlepora. That one species must, on the ground of priority, be 

 called Millepora alcicornis. 



There are two courses open to us : either to assume that there are 

 characters still undiscovered which distinguish one species from 

 another, and on the strength of that assumption retain the old specific 

 names ; or to wait until such assumed characters are discovered before 

 recognizing more than one species. 



Of these two courses the latter appears to me to be preferable. 

 If we consider a series of specimens;, a, b, c, d, &c, are distinct species, 

 we assume that the embryo of a gives rise to a definite form of coral, 

 so like its parent a that it can be easily distinguised from the forms 

 b, c, d, &c. If, on the other hand, we consider them as modifications 

 in the form of one species, then we may consider it possible that under 

 different external conditions the embryo of d may give rise to a form 



