No. I.] MORPHOLOGY OF THE ACTINOZOA. 1 39 



I have already ('89) expressed an opinion upon the value of this 

 tribe, and my only reason for referring to it here is that Boveri, 

 though recognizing that it cannot have any phylogenetic signifi- 

 cance, retains it as useful for systematic purposes ; and further, 

 Van Beneden in his recent paper recognizes it in his discussion 

 of the phylogenetic relationships of the Actinias. I wish to 

 point out that not even on the ground of convenience is the 

 tribe to be retained. 



If we are to group all the forms I have mentioned above, we 

 shall certainly have a most heterogeneous collection. Tcalia 

 will be separated from the other Bunodidas, with which it shows 

 close affinities in many particulars, and placed close to Peachia, 

 with which it has only the remotest affinities. But, worst of 

 all, Aiptasia annulata will be separated from the other species 

 of that genus, and grouped with Sideractis, whose affinities 

 seem to lie rather with the Paractidas than with the Sagartidae. 



I cannot see any necessity in the formation of such a tribe, 

 but rather much inconvenience and inconsistency. It must be 

 concluded that such forms as Tcalia and Aiptasia annulata have 

 been derived by a modification from the typical Bunodidae in 

 the one case, and the typical Aiptasias in the other. But how 

 can this modification have come about ? Its origin can only be 

 ascertained with certainty by a study of the development of the 

 modified forms, but nevertheless possible ways readily suggest 

 themselves. The decamerous form may have been derived by 

 the suppression of the dorsal or ventral pair of the first cycle 

 of paired mesenteries, the individuals passing at one time through 

 a Peachia or Oractis condition. Should the radial development 

 of mesenteries then proceed normally, such an arrangement as 

 is found in Tealia would be produced. I do not mean to sug- 

 gest that there is any direct genetic relationship between Peachia 

 and Tcalia. It is much more probable that both have been 

 derived from a typically hexamerous form by the suppression of 

 a pair of mesenteries. This is certainly the case with Tcalia, 

 and that such has also been the origin of Peachia I shall endeavor 

 to show later on. 



In a similar manner the octamerous forms may have been 

 derived from closely related hexamerous species by a suppres- 

 sion of two pairs of the first cycle of paired mesenteries, passing 

 through, therefore, a condition comparable to that of Gonactinia. 



