PERIPHYLLIDAE. 23 



tance of the supposed homologies represented in the number and arrangement 

 of these organs than in the words of Maas : " Zudem darf vom moderneren 

 Standpunkt aus geltend gemacht werden, dass auch die theoretischen Voraus- 

 setzungen fiir solche spitzfindige phylogenetische Ableitungen keineswegs 

 geniigend gesichert erscheinen, sondern dass sprunghafte Veranderungen 

 und Vermehrungen solcher adventiven Randgebilde auch auf anderer Basis, 

 nach Gesetzen der Variation und Mutation moglich sind " (: 07, p. 195). 



Periphyllidae Haeckel, 1880. 



sens. em. Vanhoffen (: 02 a ). 



This family, according to Vanhoffen (: 02 a ), includes all Coronata with four 

 sense organs, the generic distinctions within the family being based on the 

 number of tentacles, which, so far as known, always occur in multiples of four. 

 Maas (: 03, : 07), however, has retained Haeckel's family Pericolpidae to 

 include Pericolpa, with only four tentacles. But if, as Maas himself agrees, 

 Periphylla with 3X4 and Periphyllopsis with 5X4 tentacles both belong to 

 the Periphyllidae, it seems to me irrational to separate from this family Peri- 

 colpa with 1X4 tentacles, inasmuch as in the number of tentacles this genus 

 bears to Periphylla precisely the same relation that the latter genus bears to 

 Periphyllopsis. With regard to Nauphantopsis Fewkes ('86), which Van- 

 hoffen (: 02 a ) includes in this family on the supposition that it has four 

 sense organs and 7X4 tentacles, it is impossible to reach any decision with- 

 out studying fresh material, since Fewkes was unable to count definitely the 

 number of sense organs. 



In the typical members of the family the four sense organs are interradial, 

 the four tentacles, or groups of tentacles, as the case may be, being perradial. 

 In the recently described Paraphyllina (Maas, :03), however, and in the fossil 

 genus Paraphyllites (Maas, : 06 a ) this radial arrangement is reversed, the sense 

 organs being perradial, and the central one of each of the four groups of 

 tentacles interradial. Their closest relationship is with Periphylla ; they 

 must be regarded, I believe, as offshoots of that genus. 



It appears that Periphylla may be derived from Pericolpa by the devel- 

 opment, in each quadrant of the margin, of a new adradial tentacle on either 

 side of the primitive perradial tentacle; and arguing from this conclusion it 

 is reasonable to assume that Periphyllopsis in the same manner is derived 

 from Periphylla by the development of a new tentacle on either side of each 

 tentacle group of the latter genus. Whether or not this has actually been 



