40 ALTEUNATE GENERATION 



which the theory was founded, and partly by interpreting 

 them in another way. 



The former was attempted especially by Meyen,* who 

 in his voyage round the world was so unlucky as not to 

 meet with a single solitary salpa containing a chain of 

 embryos, although, free swimming salpa-chains in many 

 places surrounded the ship in masses. He consequently 

 attempted to make good the assertion, that the free 

 swimming salpa-diains and the associated embryos, which 

 Chamisso had observed in the solitary Salpfs, were to be 

 explained in entirely different ways, and had no relation 

 to each other. His observations, which were vdthout 

 doubt superficial, led him to conclude that the associa- 

 tion of the Salpa was a voluntary act, and that they had 

 the power of reuniting themselves, after having been once 

 separated. 



The opposite course is followed by Prof. Dr. Eschricht, 

 in a copious memoK lately published in Copenhagen,! ^^ 

 which he industriously tries to give another explanation 

 of the phenomena : on which account we must subject his 

 labours to a strict examination. In the first twenty sec- 

 tions, he adduces numerous anatomical relations, and re- 

 views them with as much accuracy as the examination of 

 specimens preserved in spirit will allow, and in the twenty- 

 first and following sections comes to the question, the so- 

 lution of which is the true object of the essay, namely, 

 the real nature of the associated embryos and Salpa-chains. 

 The examination of Salpa cordiformis, a solitary Sal^ja, 

 and of Salpa zonaria, an associated one, led Eschricht to 

 the conclusion, which agrees with the views of Chamisso, 

 that every Salpa chain originates in the embryo (p. 378,) 

 and consequently is born in the associated form, because it 

 is certain that the catenation of several Salpce commences 



* Meyen. Beiträge zur Zoologie, gesammelt auf einer Reise um die Erde, 

 Iste Abth., über die Salpen; Nova actaAcad. Cses. Leop. Car. natur. Cimos. 

 torn, xvi, pars prior. 1832. 



t Anatomisk-physiologiske Undersögelser over Salperne, af Dr. F. Es- 

 chricht, in den Sclu-iften der Königl. Dan. Ges. der Wissench., natui'h. og 

 mathcm. AbhancU. viii. 1841, p. 297-392, tab. 1, v. 



