of the Polypes and of their Polypary. 43 



zoologists have been led to assume that the wall was first 

 developed, and that t'rom it there originated first of all six septa 

 at the same time, that these six primary laminse, retaining 

 the advance given to them by their age, were the largest septa 

 in the adult, and so on for the septa of the second and third 

 to the nih. size. From this we have the admission of cycles 

 the age of which was shown by the size of their elements. 

 Nothing of this kind ever occurs in the embryo of Astroides or 

 of the Bcdanophyllke ; and I have numerous examples of very 

 young individuals all having twelve equal septa before possess- 

 ing any wall, and in which the formation of cycle after cycle 

 of six elements is not admissible. 



It is no longer possible to admit that the septa originate 

 from the wall, and to give the latter the preeminence over all 

 other elements of the calice, since the septa are already well 

 formed when there is no ti'ace of a wall. 



Thus as regards the first two cycles the laws according to 

 which the absolute and relative moment of appearance of the 

 septa and their origin as dependent on one of the elements of 

 the calice were supposed to be governed have no foundation 

 (raison d'etre) ; and yet it was especially for these two cycles 

 that these laws were accepted and most easily verifiable. 

 With regard to histological origin it does not seem to us to be 

 possible, at least in the embryo and the species investigated, 

 to continue to attribute it to the dermic layer. 



We recognize, therefore, at the origin of the polypary, a 

 rule which does not fail with regard to the mode of multipli- 

 cation of the tentacles in the Actiniaria without polyparies ; and 

 it is as follows : — The number of parts in accordance with a 

 certain typical number is first formed ; afterwards, a greater 

 growth being manifested in certain of these formed parts, there 

 results from it a symmetry which nothing could lead us to 

 foresee if the embryo had not been followed from moment to 

 moment. 



It is thus that the tentacles of the' Actinue. which we find 

 sometimes arranged so regularly in successive cycles in ac- 

 cordance with the type 6 (6 of the first, 6 of the second, 12 of 

 the third, 24 of the fourth, and 48 of the fifth magnitude) are 

 far from having been developed 6 at a first period, 6 at a 

 second, 12 at a third, and so on. The number 12 was first 

 produced, passing successively tlirough the inferior numbers 

 2, 4, 6, and 8 to 12. After its production the sizes alternately 

 remained stationary in 6, and increased in 6 others. Then, 

 but only then, was manifested the radiate symmetry with two 

 cycles apparently of different ages, as indicated by the relation 

 (6, + 6,). 



