208 NATURAL SCIENCE. Sept., 1893. 



adoption of a new function, or, (c) disappearance. As we have seen, 

 the first and third of these alternatives take place frequently in 

 Haliclystus, which, perhaps, more than any other Lucernarian remains 

 most closely related to the old form. 



In some species, however, e.g., Lucernaria campanulata, the third 

 alternative has been unmistakably adopted, accompanied, too, by the 

 very significant fact that, though absent in the adult, yet the marginal 

 bodies do exist for a short period in an early stage of life. (It may 

 be that the genus comprising this species is directly descended from 

 Haliclystus.) 



As to the second alternative— the adoption of a new function — 

 probably in Haliclystus there is indeed a secondary one coming, or 

 come, into operation. In this genus, the marginal bodies are used, 

 apparently, as accessory to the ordinary tentacles in holding on to 

 any prey in course of capture. Thus, if with a pencil point one of the 

 marginal bodies be touched, it adheres strongly to the pencil, and with 

 very perceptible power. Coincident with the loss of sensory organs, 

 there has been decay of the whole nervous system, the purpose for 

 which departed with the cessation of rhythmic motion and the lost 

 utility of the tentaculocysts. 



The view I have above put forward as to the relationship and 

 descent of the Lucernariae is expressed in " tree " form as follows, and 

 shows clearly on comparison with the diagram given at the commence- 

 ment wherein the divergence from the old view consists : — 



Strobilating Scyphomedusae 



with free-medusa stage Hydromedusae 



\ / Lucernaria / 



\ 



Haliclystus 



\ / 



\ / 



\/ 



Common ancestor of both Scypho- and Hydro-medusae. 

 Dr. Hurst has arrived independently and simultaneously at 

 conclusions which, I believe, are practically the same as above put 

 forward, but as I know but the outlines of his reasoning, the reader 

 is referred to his article on the subject following this (pp. 209-217). 



REFERENCES. 



1. Agassiz, L. — Contributions to Nat. Hist, of the U.S. of America, vols. 



iii. and iv. Boston, 1862. 



2. Lankester, E. Ray. — Encyclo. Brit, article Hydrozoa. 



3. Hurst, C. Herbert. — Biological Theories, V. Natural Science, vol. ii., 



part 16. 



4. Hornell, James. — Abnormalities in Haliclystus. Ibid., vol. iii., part 17. 



James Hornell. 



