THE SPECIES OF THE GENUS MILLEPOEA. 139 



conclusion that in slow-growing Millepores in unfavourable situations 

 the cycles are distinct, and that in fast-growing specimens in good 

 situations the polyps are formed in such great numbers that the cycles 

 become confused. 



(4) The Presence or Absence of Ampullce. — The ampullae of Millepora 

 were discovered by Quelch in a specimen obtained by the ' Challenger.' 

 He found a new species for the specimen, which he called M. murrayi, 

 and used this feature as an important specific character. 



I have found that ampullae occur in plicate, ramose, and digitate 

 specimens, and, as will be explained later, the absence of ampulla? in 

 any particular specimen merely means that at the time it was taken 

 it was not in a state of sexual activity. 



It is greatly surprising how very rarely specimens are found in this 

 particular condition, but I believe that it must occur in all varieties at 

 one time or another in their life-history. 



(5) The Texture of the Surface of the Corallum. — The species M. 

 verrucosa of Milne-Edwards, M. tuberculata of Duchassaing, and M. 

 striata of Duchassaing and Michelotti have been named after the 

 peculiarities of their surface. 



I have had an opportunity of examining a very fine specimen of a 

 Millepore, resembling very closely the type of M. verrucosa, and I 

 found that on the summit of a very large number of the verrucae there 

 is a small hole of the shape of a keyhole, which leads into a cavity 

 formed by a parasitic cirripede (probably Pyrgoma milleporce). On others, 

 however, no such evidence of parasitic interference with normal growth 

 is apparent from the surface, but nevertheless there is reason for be- 

 lieving that the tubercle may have been due to hypertrophy of the 

 Millepore at a spot which was irritated by some parasite, the parasite 

 subsequently being overwhelmed or killed. 



Now it is not cirripedes alone which attack Millepores ; various algae, 

 worms, crabs, and other creatures settle on the Millepores and cause 

 profound modifications of their growth. 



I think there is very good reason for believing that the warts, 

 tubercles, ridges, and the like which occur on the surface of these 

 corals are primarily due to parasites or to some other irritant, and that 

 it is very doubtful whether they are ever of specific value. If they are 

 to be used, however, it will be found that they lead to many difficulties, 

 as it is not infrequently the case that one side of a lamella is tuberculate 



