126 McMURRICH. [Vol. V. 



to describe the important features of these forms, and, at the 

 same time, to set forth my views upon the relationships of the 

 various tribes of Actinians, and the affinities which they bear 

 to the other Actinozoa. 



The advances which have been made during the last few 

 years in our knowledge of the Actinians have been very remark- 

 able, and have been largely due to the scientific expeditions sent 

 out by various governments. A number of adult forms of great 

 phylogenetic importance have been discovered, the structure of 

 known forms has been more accurately studied, and, at the 

 same time, embryological observations have given a significance 

 to structural peculiarities, and have pointed out the proper lines 

 for future investigation. As a result of these factors, we are 

 now able to picture, with a tolerable amount of assurance, the 

 phylogeny of many groups of the Actinozoa. Much still re- 

 mains to be done, however, and it is hoped that the present 

 paper will form one more step in advance, and bring the goal 

 which is sought a little nearer. 



I propose in the first place to call attention to certain phe- 

 nomena in the formation of the mesenteries, and to describe 

 some observations bearing upon their arrangement and order 

 of appearance in certain groups of the Actinozoa, and in the 

 second place I shall discuss the relationships of the various 

 groups to one another, and so endeavor to deduce their phy- 

 logeny. 



I. EDWARDSL'E. 



Very little is known at present concerning the development of 

 the Edwardsiae. Mark ('84) has figured some stages of a larval 

 Edwardsia which is found parasitic in the Ctenophore, Mnemi- 

 opsis Leidyi, Ag., of our Eastern Coast, and Boveri has described 

 the larva of Edzvardsia Claparedii. I have been able to exam- 

 ine the larvae of the Ctenophore parasite, infested specimens of 

 Mnemiopsis having been very abundant at Wood's Holl, Massa- 

 chusetts, during the summer of 1888, but none of the specimens 

 at my disposal throw any certain light upon the sequence of 

 formation of the mesenteries. Notwithstanding the very great 

 variation in size of the parasitic individuals, all those I obtained 

 were in the same stage of development, possessing eight perfect 

 mesenteries, one pair only, the ventrolaterals, being provided 

 with mesenterial filaments. 



