216 NATURAL SCIENCE. Sept., 



Some years ago I obtained from Mr. Bolton a large number — 

 probably nearly two hundred — of specimens of so-called Lucevnavia, 

 which, he informed me, had been collected on the coast of Cornwall, 

 and they were forwarded alive on some red alga?. They were all 

 small — it was autumn — and I then noticed that they were of two 

 kinds — Haliclystus and Lucevnavia- — mostly Haliclystus. I had not 

 considered this problem then, and simply took them to be two genera 

 mixed, and thought no more about it. I did not examine them closely, 

 and hence cannot say whether intermediate forms with less than the 

 full number of marginal bodies were present or not. The naturalists 

 at Plymouth may well take that problem in hand and decide for us 

 whether Lucevnavia and Haliclystus are generically — to say nothing of 

 specifically — distinct or not. 



Whatever answer may be given, Mr. Hornell's description of 

 Haliclystus must be enough to convince any non-evolutionist — if such 

 a zoologist still exists — of the mutability of species (or genera). It is 

 a simple description of a species in the very middle of its transforma- 

 tion — Haliclystus is in the very process of being transformed into 

 Lucevnavia, there, on the coast of Jersey ! 



On receiving my friend's paper I at once wrote to him, giving 

 him an outline of the above argument, and pointing out the remark- 

 able way in which his observations fitted in with my conclusions, and 

 was not a little surprised to receive, by return of post, a long letter, 

 in which he showed how he had, by an altogether different line of 

 reasoning, come to the same conclusion as my own, viz., that Hali- 

 clystus is a " degenerate " scyphomedusan — an "arrested scyphistoma " 

 — and that Lucevnavia has gone further in its " degeneracy." 



If, however, such a " degeneration " or " arrest " may occur once, 

 it seems probable that it may occur often. There may be a well- 

 established genus, Lucevnavia, to which new species are now being 

 added, not by the modification of the old one or ones, but by new 

 " degenerations " of scyphomedusae, or new " arrestments " of scyphis- 

 tomata of various species of medusae ; and hence existing well- 

 established species of Lucevnavia (supposing there ave such) may have 

 arisen, not from a common ancestral form of Lucevnavia at all, but by 

 a series of separate "degenerations" of scyphomedusans through a 

 Haliclystus stage. Or, on the other hand, it may be that Lucevnavia 

 and Haliclystus are only names for different forms of " monstrous " 

 scyphomedusa, arrested in the scyphistoma stage — that is, arrested 

 so far as strobilation is concerned, but developing the reproductive 

 organs. 



I would submit, therefore, the following conclusions for 

 criticism : — 



(i.) That Haliclystus is a degenerate or arrested scyphistoma 

 (cf. axolotl !) ; 



(2.) That its marginal bodies are avvested vudimcnts {i.e., vestiges) 

 of tentaculocysts ; 



