MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 509 



lar disk, surrounded by a single system of tentacles; and in the difl'erent polyps of anj' colony 

 all stages can be traced in the separation of the results of fission. It is therefore a verj^ favor- 

 able species for the study of polypal fission. G. von Koch (1890) has already described the 

 process as it occurs in the coralluni of the nearly allied species, Fav'ia camernom. 



Fortunatelj', also, in F. fiHujuin a complete series of stages illustrating the development of 

 the mesenteries within the larva and young polyp is available, a series extending from the larva 

 with only one pair of complete mesenteries to polyps with such a nimiber as results in fission. 

 The oldest stage reached )iy the mesenteries of the simple polyp is represented in fig. 15y, but the 

 earlier stages may be briefly noted (figs. 15 («-/'). 



The twelve primary mesenteries are all developed at or shortly after the time of settling, 

 when the larva exhibits the conditions represented in fig. \ad, four pairs of mesenteries complete 

 and two pairs incomplete. Free swimming larvas, extruded from mature polj'ps, ai-e readilj^ 

 obtained, but can with difficult}^ be induced to settle, and development proceeds very slowly. 



Fig. 15c. 



JliriVi /raflum.— Young polyp with four pairs of metacnemes (A, A; B, B). Tlie succession of the second-cycle mesenteries is bilateral, from 



the dorsal to the ventral aspect (<^. PI. xiv, fig. 109. ) 



However, on foi'eign objects, such as dead coral or old shells, to which the mature colonies are 

 adherent, young polyps ai'e sometimes found in difl'erent stages of development. These have 

 grown from larvffi which on extrusion settled around the parent, and it was from such larval polvps 

 that the stages represented in the text figures were taken. 



Fig. 15(^ is fi"om a young polyp in which four isocnemic pairs of mesenteries are present, in 

 addition to the primary twelve. In the upper stomodasal region all the latter are inserted on the 

 stomodival wall, but the fifth and .si.xth pairs tjecome free before the termination of the stomo- 

 dieum is reached, and at this place the protocnemes are in exacth' the same condition as in fig. \ad. 

 The four pairs of new mesenteries are situated within the dorsal and middle primary exoccelcs 

 on l)oth sides of the polyp, and the dorsal pairs are somewhat further developed than the mid- 

 dle pair.s. 



Vol. S— No. 7 8 



