ACALEPU^. 161 



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

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

 larger acalephaj. 



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

 class Acahphcc, 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- 

 •panularia and Coryne, and a few analogous cases of compound 

 polypes with medusiform oviparous individuals. 



The cockchaifer lives laboriously three dark years under ground, 

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

 a few merry weeks in tlie 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 empty 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- 

 panularia 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 tiie 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 larvna 

 of the medusa-pi'oducing polypes ; and the analogy is both true and 

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

 motive male and female medusae 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, Avhich 

 is this : to regard as the tj'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 

 Cynncea. 



The bell-shaped medusoid which Dalyell saw struggling to escape 



M 



