Morphology of the Madreporaria. 97 



Madrepora colonies are recognized — M. palmata, M. cervi- 

 corm's, and 31. proUfera. The late George Brook (1893) 

 regarded all these as but formce or varieties of one species; 

 Gregory (1895, 1900) at first accepted Brook's suggestion, 

 but, following upon a visit to the West Indies, reverted to the 

 Lamarckian arrangement of the specific distinctness of the 

 three; Vaughan (1901) follows Brook in considering them as 

 only varieties of one species; Verrill (1901) agrees with 

 Brook and Vaughan. So far as my own observations upon 

 the living polyps extend, and upon their anatomy and 

 histology, there are no differences of importance among the 

 three types of growth, and a discussion of their specific recog- 

 nition or otherwise becomes restricted to the peculiarities of 

 form assumed by the skeleton. 



The radial polyps of all the West-Indian Madrepores are 

 characterized by the presence of only twelve tentacles, six 

 entoccelic and six exocoelic, forming a single cycle, and 

 usually varying in size in such a manner as to suggest larval 

 relationships. On almost an^^ colony, whether of the arbo- 

 rescent or palmate type of growth, polyps are occasionally 

 met with which are slightly larger than the others and bear 

 tentacles beyond the usual twelve, any even number from 

 sixteen to twenty-four being represented. As the number of 

 tentacles on any polyp is an indication of the number of 

 internal mesenteries, it was to the polyps possessing more 

 than twelve tentacles that attention was directed. 



To procure these for microscopic examination involved con- 

 siderable labour and care. The polyps of Madrepora are so 

 small that the tentacles can only be counted with the assist- 

 ance of a lens, and then only when in an expanded condition. 

 Among a hundred polyps perhaps only one would display 

 more than twelve tentacles, and on some colonies, especially 

 those living near the surface, no such examples whatever 

 would be found. By carefully chipping around the desired 

 individual it could be isolated on a fragment of tlie colony of 

 suitable size for study. The polyps were killed in corrosive- 

 acetic or in formol, afterwards transferred to alcohol, then 

 slowly decalcified with hydrochloric acid, and stained and 

 sectionized. 



The radial polyps and corallites of Madrepora are, as a 

 rule, oval in section, the axial-abaxial diameter being the 

 longer (fig. 1). The polyps with from sixteen to twenty or 

 more tentacles were still more elongated, but with the longer 

 diameter at right angles to the axial-abaxial plane (fig. 7) , 

 the tentacles still forming a single uninterrupted cycle all the 

 way round. Two oral apertures were present on the disk of 



