42 ALTERNATE GENERATION 



identically the same solitary SalpcB which had been pro- 

 duced by the associated ones. Thus, according to Prof. 

 Eschricht, they may be born in the associated form from 

 solitary parents, and after producing a solitary progeny, 

 may themselves become transformed into solitary Salpa, 

 and in this condition may produce young in the associated 

 form. As long as these objections are unanswered, it 

 would be prudent, according to Prof. Eschricht, to assume 

 another mode of explaining these extraordinary facts, 

 " and which would accord better with the general laws 

 of development," and he ventures to propose for further 

 inquiry, the following theory of the propagation of the 

 SalpcB : 



" The Salpce in their younger state produce solitary 

 embryos, and in their older, associated ones. They do 

 not necessarily undergo any metamorphosis ; the single 

 (solitary) embryos assume, while still within the mother, 

 their permanent form ; but the embryos forming chains, 

 are slightly anomalous in figiu"e owing to their union, and 

 this form afterwards changes into that which is perma- 

 nently retained." It is vain, however, to look upon this 

 as a natiu'al explanation ; and, even if some observations 

 of my own of analogous phenomena, and the information 

 afforded by the observations of others upon similar sub- 

 jects, had not led me to consider Chamisso's theory as 

 not unnatural, still I should feel myself compelled in the 

 name of Nature, to protest against that of Eschricht, when 

 it demands to be considered a natural one, either abso- 

 lutely, or in comparison with that of Chamisso. 



Eschricht has referred his theory to " a closer examina- 

 tion ; " to which we will now subject it. " When young, 

 the Salp(je produce a solitary progeny, and when older, 

 an associated one." This expression assumes in the first 

 place, that one and the same animal, at two different 

 times or periods of its life can produce young differing in 

 no slight degree in their organization. It is true, that 

 birds when young lay fewer and smaller eggs, and when 

 older more and larger ones ; that probably certain rep- 



