212 NATURAL SCIENCE. Sept., 



bodies in question are useful, or (2) that the evolution has been inde- 

 pendent of Natural Selection. Few will be willing to accept the 

 second hypothesis — I least of all, for I believe more thoroughly in 

 the adequacy of Natural Selection than even Mr. Wallace, to whom, 

 with Darwin, we owe the theory itself. 



If, however, we adopt the first hypothesis (provisionally), we 

 must further suppose that a portion of the genus Lucernaria has been 

 isolated — geographically or otherwise — and so protected from the 

 action of the selection ; otherwise the evolution of the new genus 

 {Haliclystus) from the old one {Lucernaria), under the direction of 

 Natural Selection, would, of course, involve the extinction of the old 

 one. 



Lucernaria and Haliclystus are, however, found in the same seas, 

 though their geographical ranges may differ considerably. As to the 

 geographical distribution of any one species of Haliclystus or of Lucer- 

 naria, I will not venture to speak, for I am not sure that we can yet 

 say with certainty what are, and what are not, distinct species (or 

 even genera) in this family. For present purposes it is sufficient that 

 forms which have been called Haliclystus, and others which have been 

 called Lucernaria, are found on both east and west coasts of the North 

 Atlantic, as well as elsewhere, and that some zoologists consider that 

 some of the American specimens in both genera are specifically iden- 

 tical with some of the European ones ; and since the mode of life is 

 the same in both, and both live on Zostera, and on red sea-weeds, 

 just below low-water mark, there arises a very serious difficulty in the 

 way of the assumption of isolation, either geographically or otherwise. 

 Though the marginal bodies are, perhaps, not very complex bodies, 

 yet, in comparison with the whole body of the animal, they are suffi- 

 ciently complex to justify the assumption that Natural Selection could 

 only determine their evolution during a very long and very severe 

 struggle for existence and for multiplication. 



The organs may give some slight advantage, or even a great 

 advantage, to Haliclystus. They may serve, for instance, as " anchors " 

 (Clark) (i) ; but that is not enough. It Natural Selection has caused 

 the evolution of animals possessing those organs (Haliclystus) from 

 animals not possessing them (Lucernaria), that means that the organs 

 have at every stage in their evolution conferred such an advantage 

 on their possessors as to enable them to vanquish, to starve out, to 

 render extinct, the forms not possessing them, orpossessing them only 

 in a less perfect state of development. It means that the evolution of 

 Haliclystus from Lucernaria would have exterminated the genus 

 Lucernaria in the seas where this evolution occurred ; and this the 

 geographical distribution of the two genera emphatically contradicts. 



We may therefore regard — nay, we are compelled to regard, the 

 evolution of Haliclystus from Lucernaria as disproved. 



From what, then, is Haliclystus descended ? 



I believe the clue to the solution of this problem is to be found in 



