4 



Mr. S. J. Hickson. 



cannot be used as the diagnostic character of any one species, since 

 these structures occasionally occur in nearly all the principal forms of 

 the genus which have been described. It was not until I examined one 

 of the many specimens of the genus collected by Mr. Stanley Gardiner 

 in Funafuti, however, that I had the opportunity of seeing again a 

 male medusa, all the other specimens I had received having proved to 

 be barren. The male medusae of Mr. Gardiner's specimen turned out 

 to be identical in size and form with those given to me by Professor 

 Haddon, and I came to the conclusion that no specific distinction could 

 be drawn between the two forms based on characters of the medusa 

 before it is set free (3). 



In May, 1898, Mr. Duerden, of the Jamaica Institute, sent me a 

 small piece of Millepora preserved in spirit, which upon examination 

 was found to bear female medusse. Each of these medusae carried on 

 the manubrium from thirty to fifty ova of approximately equal size, 

 0"015 mm., and the general appearance of the medusae suggested that 

 they were nearly ready to escape. This appearance, however, proved 

 to be deceptive, for in December I received another consignment of the 

 material from Jamaica, in which the medusae showed very different 

 characters, three or four, or, in a few cases, five, of the ova in each 

 medusa being greatly enlarged and the others degenerate. In the 

 meantime, Mr. Duerden wrote to me saying that he had actually seen 

 these medusae escape, and had been able to liberate many others from 

 the corallum by means of a needle. Thus was it definitely proved 

 that this Millepore in the West Indies produces free swimming medusae 

 which bear ova. 



Several important questions arose when this matter was settled. It 

 was clearly important to find the male medusa of Millepore in Jamaica 

 to compare it with the female medusa and also with the Pacific male 

 medusae. It was also important, if possible, to trace the development 

 of the medusa, and to find, if possible, the place of origin of the 

 sexual cells. In the hope of being able to get fresh material which 

 would enable me to answer these and other important questions, I 

 have delayed the publication of the results I have obtained for nearly 

 twelve months, but as it seems probable that I may have to wait a 

 very long time more before the material is forthcoming, I have decided 

 now to publish the results of my investigation of Mr. Duerden's 

 material. 



1. The immature female medusce received in May, 1898. A small 

 branch of a Millepore well preserved in spirit after treatment with 

 formalin was all that was sent to me. No very definite signs of the 

 presence of the medusas could be noticed before the specimen was 

 decalcified, but as soon as the soft tissues peeled off the lower parts of 

 the corallum under the action of nitric acid a considerable number of 

 medusiform bodies could be seen with a lens. They varied consider- 



