4 G. HERBERT FOWLER. 



by V. Koch in Stylophora (2). These ellipsoids have a distinct 

 sweep from one " line of growth " to the next. 



The calyces are all of approximately the same size, and 

 that so minute as to render investigation of the anatomy 

 difficult. 



The septa are very irregular of occurrence; the complete 

 number appears to be six, but three are rarely to be seen in 

 one section, often none at all. They are not constant through 

 the whole depth of the polyp cavity, but occur as discontinuous 

 ridges (fig. 6, Ab.). In every polyp, however, either an axial or 

 abaxial septum is present, which enables the orientation of the 

 polyp to be efi'ected as in the Alcyonaria. (These terms, axial 

 and abaxial, are used in preference to the ordinary and mis- 

 leading "dorsal" and "ventral,^^ and were suggested originally 

 by Professor Milnes Marshall, ^ Trans. Roy. Soc. Edin.,' 

 1883.) 



There is no columella, but often the axial and abaxial septa 

 fuse, low down in the polyp cavity, so as to divide it into two 

 equal halves (fig. 3, a'), in a manner suggestive of the 

 " median plate "" in Pocillopora and Seriatopora figured by 

 Professor Moseley (3). 



The cost 86 bear apparently no relation to the septa in the 

 well-grown colony, whatever may have been the case in the 

 founder-polyp. Not only is no connection traceable between 

 them in a transverse section of the branch, but even in a single 

 polyp standing off from the stem, where the number of septa 

 is under the most favorable conditions but six, about twenty 

 costge surround the calicle. 



B. Anatomy. — The whole of the corallum is covered exter- 

 nally by a definite body wall of ectoderm, mesoderm, and 

 endoderm (fig. 6, ext, b. w., fig. 4, ect, me. en.), immediately 

 beneath which lie, as in Rhodopsammia, external longitu- 

 dinal canals parallel to the long axis of the corallum (figs. 

 3 4, 6, c^). These, however, are not the result of the same 

 anatomical relations in both cases ; in Rhodopsammia, lamellse 

 of mesoderm with a layer of endoderm on each side are given 

 oflF from the external body wall, and unite with the endoderm 



