THE EBWAEDSIA-STAGE OF LEBBUlSriA. 301 



their full significauce only from a comparison with the tetrameral 

 Scyphomedusae. Commenting upon the connection of this group 

 with the Zoantharta Haddon, ten years ago (1889), wrote : — 

 " The relationship of the Hydra-tuba and Seyphostoma stages 

 of the Scyphomedusse (Acalephse) to the Zoantharia is now 

 generally admitted, iudeed a group (Taeniolatse) has been erected 

 by Professor E. Hseckel to include them both. Later Professor 

 A. Gotte has similarly proposed the term Scyphozoa for the 

 same assemblage, but including the Ctenophora, as opposed to 

 the remaining Coelenterata or Hydrozoa. Tha Seyphostoma 

 have an oesophagus liued by ectoderm (Stomodseum), four glan- 

 dular mesenteries, the edges of which are true craspeda, and 

 serve to digest food; in their upper portion nematocysts are 

 present. The four tentacles are afterguards increased to eight, 

 and finally to sixteen. It is especially noteworthy that at first 

 there are only two tentacles : probably this is a reminiscence of 

 a remote ancestor. The widespread occurrence of a symmetry 

 of four amongst the larvae of the Scyphozoa is very suggestive." 



Discussing the Phylogeny of the Actinozoa McMurrich (1891 a, 

 p. 149), two years later, also remarked: — "As regards the rela- 

 tions of the Actinozoa to other Coelenterates, there is little to 

 be said ; the majority of authors who have committed themselves 

 upon the subject, agree in tracing the Actinozoan stem back to 

 a form similar to the Scyphistorna. The evidence we have seems 

 to point in that direction ; but it must be acknowledged that it 

 is exceedingly scanty, and there are many points of difference 

 between any Scyphistorna of which we have a description and 

 the simplest Actinozoa. It seems probable, however, that the 

 Actinozoa are to be traced back to an ancestor possessing only 

 four mesenteries. The occurrence of an octameral symmetry in 

 the simplest Actinozoa seems to point in that direction, as well 

 as the fact that, in the development of the Hesactinise, the 

 stage with four mesenteries seems to mark an epoch, much less 

 distinct, however, than that indicated at the close of the 

 JjJdivardsia stage." 



The tetrameral symmetry of the Lehrunia larva, perfect as 

 regards the tentacles, and the mesenteries and ccelomic diverti- 

 cula of the upper archenteric region, seems to be explicable only 

 on such a throwing back of the ancestry of the Zoantharia. The 

 two alternating series of four tentacles exactly recall the eight- 



LINN. JOUEX. — ZOOLOGY, YOL. XXYII. 23 



