OF THE ACALEPH.E OF NORTH AMERICA. 227 



pellatiou of Silk-worm, for instance, to that animal evo., in its chrysalis and motli con- 

 dition, because it is best known in the form of the silk-producing worm under that name, 

 so should we now adopt one single systematic appellation for all the phases ot growth 

 of those animals which undergo alternate generations, of course adopting as that winch 

 is to be preserved the oldest name under which the animal was first noticed, whether 

 in its free condition or in the fixed state of its earlier metamorphosis. 



I am well aware, that many inconveniences will arise from such a practice ; and 

 that names with which we are most ^miliar will have to give place to others less gen- 

 erally in use; but there is no safety in nomenclature without absolute adherence to the 

 law of i)riority. Just as we discard for ever the recent appellations of so many young 

 animals which have been of late considered as peculiar types, because we recog- 

 nize them as mere embryonic conditions of well-known animals, so should we select the 

 older name whenever we (iud that the adult male and the female of an animal, or the 

 youii- and the adult state, have been described as two distinct species. We preserve 

 the imme of Larus marinus because it is the older, not because it is the more appropri- 

 ate, of the different names under which the various plumages of our large marine gull 



have been described. 



There can be no hesitation in the present case. The stemmed and fixed genera- 

 tion of our Medusa had been known and named long before its free Medusa form was 

 ascertained. We shall therefore unhesitatingly discard in time the generic name of Sarsia, 

 though no one is more desirous than I am to see the name of Sars proclaimed as one of 

 those who have contributed a large share to the advancement of our science. There is, 

 however, a difficulty in introducing at once a change in this case, since the Coryn^ have 

 been subdivided into so many genera of late, as to render it almost impossible to decide 

 which of them should be preserved and to which all the different species now known be- 

 lono The difficulty is fi.rther increased by the claims which Dr. G. Johnston has re- 

 cency raised in favor of some older names which had been disregarded by modern writers. 

 1 Nvould also urge the necessity of a detailed description equally complete of the 

 various phases of life of these animals, and would propose to introduce these details 

 under distinct heads so far as to preface the descriptions by the designations of Proles 

 pohjpoidea and Proles medusina. 



It is a matter of great difficulty to ascertain the specific identity or difference between 

 animals of this class, and, I must confess, I could hardly venture to decide, in the present 

 case whether Sarsia tubulosa of the British coast, and those specimens which Dr. bould 

 has identified with the European, be truly identical or specifically distinct. Ihere are 

 nearly as many reasons to be given in favor of their identity as for their specific difference, 



