256 OS THE 8PECIKS OF MILI.EPOHA. [Apr. 5, 



In the large collection at the British Museum only a few specimens 

 exhibit ampulla\ 



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

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



Gciural Considerations. — It appears to me that theseinrestigations 

 present very sti-ong reasons for believing that there is only one 

 species of Millepora. That one species must, on the ground of 

 priority, be called Millej^iora alcicoi'nis. 



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, ff, 6, 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 distinguished 

 from the forms h, 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 a 

 may give rise to a form similar to 6, or c, or d, or any intermediate 

 or combined form of these varieties. 



By the former course we are pi-actically denying the possibility 

 of considerable plasticity ; by the latter course, while not assuming 

 that it exists, we do not deny it, 



jSTow the evidence in favour of the view that the Millepores are 

 extremely plastic in their growth increases with every new 

 collection that is examined. Nearly every large specimen shows 

 some branch or plate that is distorted, twisted, compressed, or bent 

 into a different shape from the rest of the coral ; its surface shows 

 galls, cups, tubes, warts for the accommodation of crabs, worms, 

 cirripedes, algae, and other so-called parasites. Nor is there any 

 greater constancy of form in the smallest independent specimens 

 that can be found. They may be simply incrusting, or may form 

 a simple crest, or a short pointed process from the base, according 

 to the character of the object on which they grow. It is therefore, 

 in my opinion, not only extremely inconvenient but positively 

 erroneous to consider those forms of gro\^th that may be grouped 

 round one " type " as a species distinct from those that can be 

 grouped round another " type." By this plan we either deny the 

 extreme degree of variability which there is reason to believe does 

 occur in nature, or else we employ specific names in a sense alto- 

 gether different from that in which they are used in the other 

 groups of animals and plants. 



It w^ould be premature to propose to extend my remarks to other 

 genera of corals, but I have already pointed out that there are 

 some reasons for believing that there is not more than one species 

 in the Alcyonavian genus Tubipora and the Hydrocoralline Disti- 

 chopora. Our knowledge of the soft parts of Madrepm-a and other 

 genera of Zoantharian corals is so small that it is possible that in 



