Haddon — The Newly- JEEatched Larva of Euphy Ilia. 133 



first and the succeeding pairs of mesenteries. To put it briefly, this 

 difference consists in the fact that in the first pair of mesenteries the 

 ectoderm of the stomatodseum applies itself directly to the body- 

 wall, and pushing aside the endoderm comes into contact with the 

 basement membrane (mesogloea) of the ectoderm of the column. 

 Thus the first formed portion of the mesentery is its filament ; the 

 mesentery proper subsequently grows out into the coelenteron. The 

 succeeding mesenteries first project 'from the body- wall, come into 

 contact with the stomatodseum from above downward, and push 

 before them a portion of the reflected ectoderm which has grown 

 round the free end of the stomatodseum and up its coelenteric 

 surface. This band of ectoderm is carried down the free end of the 

 mesentery in its downward growth as its filament (oraspedura 

 of Gosse). 



The next stage described by Wilson is one in which there are 

 six primary or perfect pairs of mesenteries and six secondary 

 or imperfect pairs; they all possess filaments. It is thus highly 

 probable that the order of appearance of the mesenteries in 

 Manicina precisely resembles that of the typical Actinise. There 

 is, however, one discrepancy between Wilson's observations and 

 those of de Lacaze-Duthiers, as the former says : — " According to 

 Lacaze-Duthiers, the fourth pair appears between the first and 

 second pairs. The Hertwigs suggested (?), on general grounds 

 of symmetry, that the order of appearance was as I have figured. 

 As regards the fifth and sixth pairs, however, the old account 

 of Lacaze-Duthiers holds for Manicina as against the figures given 

 by the Hertwigs for Adamsia" [I. c. p. 212). 



This point requires to be reinvestigated in the forms studied by 

 the French savant. For in all the larvse I have seen the second 

 pair (of Hertwig and Wilson) is better developed and bears larger 

 mesenterial filaments than the fourth pair (Lacaze-Duthiers' second 

 pair). I have elsewhere alluded to the fact that in Halcampa 

 chrysanthellum only six mesenteries bear generative organs, these 

 being the pair of sulcar directives and the sulcular mesenteries of 

 the two perfect lateral pairs ; the sulcular directives and the sulcar 

 elements of the perfect lateral pairs of mesenteries being sterile. 

 The fertile mesenteries are thus the first, second, and third pairs of the 

 new enumeration ; these too are the only mesenteries which possess 

 mesenterial filaments in our Euphyllia larva. Mark (1884, p. 44, 



