552 A. FRASER DIXON. 



The sections which I made at this time showed that the 

 Hertwigs' assumption was incorrect, and that Lacaze-Duthiers 

 was right in his determination of the first eight mesenteries. 

 They showed that the two mesenteries assumed by the 

 Hertwigs to be formed very early — in fact, to be the first 

 formed — were not present at all in the eight-mesentery stage, 

 but only arise as this stage is passing into the twelve-mesen- 

 tery stage. The sections confirmed Lacaze-Duthiers that 

 the four mesenteries dotted in Dr. Fowler's Fig. A were the 

 latest developed. Unfortunately I was not able to obtain 

 specimens younger than these with eight mesenteries, and so 

 made out nothing regarding the order of appearance among 

 these eight. Professor Haddon, however, in his "Eevision^' 

 (^Sci. Trans. Roy. Dub. Soc.,' vol. iv, series 2, p. 350) states, 

 " In these representative species of three different families of 

 Actiniae the development of the mesenteries is similar in all, 

 both as regards the order of their appearance and the dis- 

 position of their muscles, and they are also identical with those 

 of the larva of Halcampa." This from my observations is too 

 wide a statement, and it would only have been safe to say "in 

 these three species the disposition of the first eight mesenteries 

 is similar to that found in Edwardsia and in the larva of Hal- 

 campa, the arrangement of the muscle plates also correspond- 

 ing ; further, the arrangement of the next four mesenteries 

 takes place in positions similar to those noted for Halcampa." 



That this was really the point on which Professor Haddon 

 wished to insist, and that he was not thinking of the order in 

 formation of the mesenteries of the eight or "Edwardsia stage," 

 is, I thiuk, certain to anyone who reads his paper on " The 

 newly hatched Larva of Euphyllia," read before the Royal 

 Dublin Society in March, 1890. In this last paper, on p. 133, 

 Professor Haddon states that the order of development among 

 these first eight mesenteries in the forms studied by Lacaze- 

 Duthiers requires re-investigation, and that in Euphyllia, at all 

 events, he has a priori reason for believing that the order of 

 Lacaze-Duthiers is not present, but that that described by 

 Wilson for Manicina obtains. Hence it is almost certain that 



