46 ALTERNATE GENE-RATION 



preceding sections, and especially in the phenomena 

 observed with regard to the propagation of Medusa 

 aurita. This free swimming Medusa always produces a 

 progeny which is polypiform, and destitute of the power 

 of locomotion, but which on the other hand after attaching 

 itself to various bodies at the bottom of the sea, brings 

 forth a progeny consisting of free swimming Medusa, 

 which never assume the polypoid form ; and this alterna- 

 tion is constant. The fact may be thus expressed : that 

 each second generation is affixed and polypoid, or that 

 the free swimming hemispherical Medusce always produce 

 a polypoid offspring, and that the polypoid Medusce are 

 always the parents of the free swimming hemispherical 

 ones, &c. I have consequently no hesitation in expressing 

 my belief, that the alternate generation of the Salpa, from 

 solitary and associated individuals, is to be explained in the 

 same way as that of the Medusa, and that the first gene- 

 ration of these animals serves as a series of foster-parents, 

 whose object is, by their furthering the development of 

 the second generation, to conduce to the perfection of the 

 species. I am, however, prepared to admit, that this 

 kind of explanation does not enlarge our knowledge vidth 

 regard to the propagation of the Saljpa ; I only think, 

 that the phenomena already known, will have a clearer 

 light thrown upon them from the analogy. Some doubt 

 even must still remain, on the circumstance whether the 

 solitary or the associated Salpa are the foster-parents. 

 In my opinion however, it is the solitary form rather 

 than the other which should be assumed to be that of the 



* Prom a remark in Sar's Memoir on the Medusce (Erichson's Archiv, 

 1841, H. i, p. 29,) I perceive that that excellent observer has instituted re- 

 searches on the development of the mlfce, and promises to communicate 

 them at another opportunity (which it is much to be desired should occur 

 soon.) Although in the above place he does not state anything precise, vpith 

 regard to the result of his inquiries, yet we may gather from what he says 

 that Chamisso's views and remarks are in the mam correct. " The mlpee 

 correspond in tliis vidth the medusce, that it is not then lance which are de- 

 veloped into the perfect animal, but the progeny of the lance ; it is not tlie 

 individual, but the generation which is metamorphosed." 



