EVIDENCES OF EVOLUTION. 117 



as appearances go, it may be that of a fish, a rep- 

 tile, a bird, or a mammal. Subsequently it exhibits 

 the characteristics of a bird or a mammal, but the 

 order to which it pertains is disclosed only at a yet 

 later period. At a still later stage, after manifest- 

 ing the characteristics of the family, genus, and 

 species of which it is a member, it acquires the dis- 

 tinguishing attributes of its race. 



Amphioxus and Loligo. 



A more striking instance of recapitulation is 

 exhibited in the life-history of the amphioxus, or 

 lancelet, interesting, among other things, for being 

 the lowest known form of vertebrate. Here, as in 

 the case of all other animals, the first stage of devel- 

 opment is a simple germ-cell. This soon subdi- 

 vides, but the subdivisions, instead of separating, as 

 occurs in many of the lower forms of life, remain 

 together and constitute what is known as the mor- 

 ula stage, because of the resemblance in shape of 

 the group of cells to a mulberry or blackberry. 

 They subsequently assume a tubular form, in which 

 condition the cells are disposed around a central 

 tube-like cavity, open at each end. This is suc- 

 ceeded by the blastula stage, in which the cells are 

 grouped together in the form of a hollow ball, the 

 outer cells being provided with cilia, thus enabling 

 the embryonic amphioxus to move freely in the 

 water. This condition is followed by a series of 

 other changes, until, finally, the animal, after numer- 

 ous and instructive transformations, acquires the 

 adult form. 



