16 METAMORPHOSES OF MAN 



and Teredo.* Apart from an author's egotism, and 

 because the earlier stages of their development are 

 more familiar to me personally than to any one else, 

 I have selected these two species for the purpose of 

 illustration. In addition to what we shall learn from 

 an examination of these, I shall describe the chief 

 features of mammalian development, but I shall not 

 allude to the ordinary ovipara, whose embryogeny, 

 seen from our point of view, would be of little 

 interest. 



As soon as the egg of Hermella and Teredo is laid, 

 whether it be impregnated or not, it becomes the seat 

 of internal changes, which do not alter its general 

 form, and which we notice, as affecting its trans- 

 parency. A mysterious power operates upon the yolk, 

 accumulating its particles, sometimes at one point, 

 sometimes at another, affecting the outer surface, and 

 exhibiting in the mass shadowy figures which alter 

 in form every moment. If we assume that similar 

 changes take place in the mammalian egg, we can 

 then understand how Messrs. Barry and Bischoff, 



* My researches on these two creatures, the first belonging to 

 the Annulosa, the second to Mollusca, were published in the 

 " Annales des Sciences naturelles" for the years 1848 and 1849. 

 In the articles on embryogeny, I laid especial stress on the changes 

 dependent on the vitality of the egg itself, and particularly upon 

 the phenomenon of segmentation which takes place even in unim- 

 pregnated ova. In 1849 I observed the same thing in Unio — 

 (Comptes rendus.) Among. the naturalists who have made similar 

 statements I may mention one, M. Vogt, whose authority in a 

 matter of this sort is very great, and who has seen segmentation take 

 place in the unfecundated eggs of Firola (referred to by Siebold in 

 his work on true parthenogenesis). 



[The latter work has been translated into English by Mr. W. S. 

 Dallas.— Ed.] 



