OF THE SALPiE. 45 



hypothesis of Prof. Eschricht leads, in my opinion, still 

 remains. He confessedly assumes, " that the embryos 

 forming the chain," change at a later period from their 

 somewhat anomalous form into the permanent one, (that 

 is, into the form of the solitary,) and at the same time 

 he supposes, as he is compelled to do both by the obser- 

 vations of living nature of Chamisso and others, and by his 

 own anatomical researches, that they, while still in the 

 first or associated condition, produce embryos (the form 

 of which is here immaterial) and then, afterwards assume 

 another and permanent form. On the contrary, however, 

 I must, fourthly, object, that it is opposed to all natural 

 considerations, to all known natural phenomena, and to 

 all physiological principles, that an animal should be able 

 to propagate itself before it has attained its perfect form 

 and development. Although Professor Eschricht may 

 assume, that the first three assertions of his hypothesis 

 are not contrary to nature, the last, at least, must be 

 considered so. 



Having thus shown that the proposed explanation of 

 the phenomena attending the propagation of the Salpa, 

 from whatever side it is viewed, is not the less unnatural, 

 we retmii to Chamisso' s theory, which is founded upon 

 the observation, that the first generation of these animals 

 is solitary, and the second associated, or, in other words, 

 that all Salpa chains are produced from solitary Salpa, 

 and all solitary Salpce on the other hand, from the associ- 

 ated. This conclusion may at first sight appear extra- 

 ordinary ; I am, however, convinced that every attentive 

 reader will find something similar displayed in the two 



long a time, and so ctiaracteristically, the form they possessed during foetal 

 life. It can scarcely be imagined that the external and iaternal conditions, 

 tab. iv, fig. 18, of an animal of the size of the Salpa zonaria should be 

 changed ■without metamorphosis into those of the Salpa cordiformis (tab. 1.) 

 Thus, according to the hypothesis of Professor Eschricht, the full grown 

 solitary mlpce must have a double origin, viz., partly as solitary from young 

 individuals, and partly as associated from older ones, and which at a later 

 period assnme the soHtary form ; but this also appears very umiatui-al, that 

 what was at the beginning dissimilar, should afterwards be developed and 

 become similar. 



