AND THE LOWER ANIMALS. 147 



connected in the young stage, were afterwards isolated, 

 and caused to assume other characters in obedience 

 to the laws of development. He thus admitted the 

 existence of true metamorphoses, for the distinction 

 between the two forms — solitary and aggregated — 

 extends not only to the external character, but also to 

 the form and disposition of the viscera. 



Chamisso discovered that this phenomenon is far 

 more complex than was supposed.* He perceived that 

 the SalpsB are both androgynous and viviparous, and 

 that they preserve their infant characters all through 

 life ; but, strange to say, a solitary mother produces 

 only individuals united into colonies, and vice versa. 

 Hence it follows, that a Salpa resembles neither its 

 parents nor its offspring, but is exactly like its grand- 

 parent and grand-offspring. The external and internal 

 characters of the alternate generations are, moreover, 

 in every respect identical. 



In this case, metamorphosis does not affect indi- 

 viduals merely, but operates on entire generations. 

 The same result is produced as if the caterpillar, 

 instead of undergoing its transformation, were to 

 produce a fully-formed butterfly, which in its turn 

 would bring forth caterpillars. It is a true alterna- 

 tion of generations, and this law holds good for all 

 biphorae.f Consequently, the species of these mollusks 



* u De Animalibus quibusdam e classe Vermium linneana. Fasc. 

 prim., de Salpis." 1819. 



f The following passages from Chamisso's memoir will show that 

 I have almost employed the very words of this naturalist, " Qua 

 reposita (Salpa bicorni), alternationem generationum legem esse, ut 

 posuimus genericum, omnibus communem speciebus, observationi- 



bus innititur Talis speciei metamorphosis generationibus in 



salpis duobus successivis perficitur, forma per generationes (nequa- 



L 2 



