ACALEPH^. 161 



progeny. But, to be consistent, the rule should be extended to other 

 medusiform progeny of liydriform polypes, and so to many of the 

 larger acalephie. 



Such a modification, amounting virtually to a suppression, of the 

 class Acalephcc, however consistent with the reasoning based upon 

 the principles which have been just laid down, would be opposed to 

 the practice of naturalists in almost every instance, except the Cam- 

 pa?iidaria and Coryne^ and a few analogous cases of compound 

 polypes with medusiform oviparous individuals. 



The cockchaffer lives laboriously three dark years under ground, 

 eroding the roots of plants, before it emerges into light, and disports 

 a few merry weeks in the bright summer sunshine, in its winged 

 state. The vermiform larva, in giving birth to the winged insect, 

 has exhausted most of its substance, and all its vital energies as such, 

 and leaves nothing but its emjDty skin behind. 



The ephemeron, after a year's obscure existence as a water-worm, 

 creeps out of the vermiform case, and uses its newly-acquired aerial 

 locomotive organs, and its procreative powers, for a brief day or 

 hour. 



We do not, however, class the cockchaffer and the may-fly with 

 the Vermes, as we ought to do according to the analogy of the Cam- 

 j)anularia and Coryne. So vast a proportion of the parent worm has 

 supplied the material to the plastic force, which has operated in the 

 re-arrangement of parts for the completion of the winged insect, that 

 we say the worm has been converted into the insect. 



The larval aphides, however, unequivocally propagate, and so 

 frequently, as quite to parallel the condition of the procreant larva3 

 of the medusa-producing polypes ; and the analogy is both true and 

 close of the winged male and oviparous female aphides to the loco- 

 motive male and female medusie and to the male and female modified 

 leaf-individuals of plants. Yet, notwithstanding these analogies, 

 another rule guides the zoologist in the majority of such cases, which 

 is this : to regard as the t^'pical phase of the species that most perfect 

 form which parallels the winged state of the insect, the medusa state 

 of the polype, and the seed-producing and pollen-bearing flower-parts 

 of the plant. And the zoologist accordingly classes the batrachian 

 and the butterfly, the chaffer and the ephemeron, the beroe and the 

 medusa, according to the structure of the last phase of their de- 

 velopment. 



Few naturalists will be found to object to this : but, to be consistent, 

 they ought not to place in separate classes the Campanularia and the 

 Cyancea. 



The bell-shaped medusoid which Dalyell saw struggling to escape 



M 



