252 



PROF. S. J. HIOKSDN OlSr THE 



[Apr. 5, 



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 and the other is not, or that one lamella 

 or branch is covered with wart-like processes and the others are 

 smooth. 



(6) The Relative Number of Dactyloporesayid Gastropores. — Finding 

 that all other characters derived from the skeleton are unsatis- 

 factory for determining and distinguishing species, I thovight it 

 possible that a good character might be found by calculating the 

 average number of dactylopores to each gastropore in a number 

 of species. 



In many specimens the cycles are so close one to another that 

 it is often difficult to determine to which cycle a particular dactylo- 

 pore belongs. In order, therefore, not to be misled, I used only 

 those cycles which were clearly defined from their neighbours. 



In the following table I have put together the results of my 

 calculations on this point : — 



Accepted specific names 

 of specimens. 



(The name of donor and 

 locality in parentlieses.) 



I. M. murraiii. 

 (Haddon, Torres Str.) 



II. M. alcicornis. 



(Brit. Mus.,W. Indies.) 



III. M. alcicornis. 

 (Shipley, Bermudas.) 



IV. M. alcicornis. 

 (Lister, Tonga.) 



V. M. plicata. 



(Hickson, Celebes.) 



VI. M. coniflanata. 

 (Man. Mus., W. Indies.) 



VII. M. alcicornis. 

 (Man. Mus., W. I.) 



VIII. M. alcicornis. 

 (Agassiis, Bahamas.) 



Number of 



cycles 



counted. 



6 



8 



(i 



12 

 12 



12 



7 

 100 



7 

 13 



Average No. of 

 dactylopores 

 in each cycle. 



5-15 

 6-45 

 5« 



6-7 



5-08 



7-08 



6-28 

 5-82 



614 



5-5 



