134 



McMURRICH. 



[Vol. V. 



Messrs. Dixon describe, but my results have not been perfectly- 

 satisfactory. I find that apparently all six pairs of mesenteries 

 of the second hexamerous cycle appear simultaneously, but that 

 the pair on each side of the dorsal directives develops more 

 rapidly than the others and soon surpasses them in size. 



The evidence from adult forms 

 yrj seems to point, however, to the 

 development of the first cycle of 

 ,-rp paired mesenteries successively. 

 I shall return to the discussion of 

 )2Ithe question later on ; in the mean- 

 time I wish to describe briefly the 

 forms which yield the evidence 

 such as it is. 



The form which shows the slight- 

 est advance upon the Edwardsia 



Fig. II.— Transverse sections through condition is Hert wig's Scytophorus 

 Scytophorus striatus. , , 



striatus ( 82), tor the reception 01 

 which he erected the new tribe Monauletz. Hertwig recognizes 

 in this form (Fig. II) a single pair of directives only ; but it is 

 to be noticed that we have at the dorsal surface two mesenteries 



(IV) with their longitudinal mus- 

 cles on the ventral faces, exactly 

 the condition which we find in the 

 dorsal directives of Edwardsiae. I 

 cannot see any reason for not 

 regarding them as the dorsal direct- 

 ives. The mesenteries present in 

 Scytophorus represent, I believe, 

 the twelve Halcampa mesenteries 

 with the addition of one mesentery 

 on each side (^) in the spaces be- 

 Fig. in. — Transverse section of tween the dorsal directives and the 



Gonaclinia prolifera. secQnd mesenteries (II) . Boved 



('90) recognizes the eight Edwardsia mesenteries in ScytopJiorns, 

 but derives it directly from that group, not disregarding, how- 

 ever, the possibility of its derivation from an Halcampa con- 

 dition, which I prefer to accept. 



In the form described originally by Sars as Actinia prolifera, 

 and more recently by Blochmann and Hilger ('88) as Gonactinia 



