110 Dr. J. E. Duerden on the 



botli tlie inner and outer lining of tlie stomodaeum, differs 

 altop;ethcr from that elsewhere liniPit^ the canals and ji^astric 

 cavity of the polyps ; the cells are columnar, strongly ciliated, 

 non-vacuolated, and stain deeply. 



Fig. 10 is from a section a little to one side of the oral 

 aperture, and reveals four mesenteries extending vertically 

 from the outer wall as far as the inturned stomodreal wall. 

 In fig. 11 the two outermost mesenteries have become free at 

 their lower extremity, but the two inner still retain their 

 connexion with the infolded margin of the stomodaeum. In 

 the next figure all the primary mesenteries are free from the 

 stomodaeum, but the one to the right is connected with the 

 inner wall of the peripheral canal. To the left of the mesentery 

 the rudiment of an additional mesentery has now appeared. 

 In the succeeding figure (fig. 13) the mesentery at the extreme 

 right has disappeared and a rudiment of a second new mesen- 

 tery occurs. Thus all the six mesenteries — four complete 

 and two incomplete — of one side of an adult polyp of Madre- 

 pora are accounted for. 



The important facts in the present connexion which the 

 series of sections serve to demonstrate are as follows : — 1. In 

 the formation of a bud of Madrepora the six pairs of mesen- 

 teries characteristic of the adult polyps are all present at a 

 very early stage, perhaps appearing simultaneously. 2. The 

 four complete pairs arise at or near the angle between the 

 disk and stomodasal wall, and extend all the way down the 

 latter, and also radiate along the outer wall. 3. The two 

 incomplete pairs arise on the body-wall (not yet differen- 

 tiated into actual disk and column) some distance from the 

 oral aperture, and from the beginning are wholly free from 

 the stomodaeum and extend only a short distance. 



The above results from the bud-polyps may now be compared 

 with the conditions occurring in the fission polyps of Madre- 

 pora. That no succession in the appearance of the new six 

 pairs of mesenteries has been met with in the numerous 

 fission polyps examined is evidently due to the circumstance 

 that, as in the bud, all the six pairs appear at a very early 

 stage, if not simultaneously. The presence of mesenterial 

 strands connecting the two stomod^eal tubes may be brought 

 about by the close association of the complete mesenteries 

 with each storaodseum at the time of separation of the latter. 

 Obviously from the insertion of the mesenteries at about 

 equal distances all round the stomodaeal wall only two adja- 

 cent members will be directly opposite each other, and, 

 arising from the same proliferating band of tissue, may grow 

 as single lamella? down the opposite aspect of each stomodjsal 



