96 



WHAT IS LIFE ? 



living edifice. Next, the mass of organic bricks, or 

 cells,' as they are technically called, thus formed, 

 acquires an orderly arrangement, becoming converted 

 into a hollow spheroid with double walls. Then, upon 

 one side of this spheroid, appears a thickening, and, by 

 and bye, in the centre of the area of thickening, a 

 straight shallow groove (fig*. 12 A) marks the central line 

 of the edifice which is to be raised, or, in other words, in- 

 dicates the position of the middle line of the body of the 

 future dog. The substance bounding the groove on each 

 side next rises up into a fold, the rudiment of the side 



FIG. 12. A, Earliest stages in the development of the dog ; B, Rudiment 

 further advanced, showing the foundations of the head, tail, and 

 vertebral column ; C, The very young puppy. (From " Man's Place in 

 Nature/' by Thos. Hy. Huxley, F.R.S!, 1864, p. 63.) 



wall of that long cavity, which will eventually lodge the 

 spinal marrow and the brain ; and in the floor of this 

 chamber appears a solid cellular cord, the so-called 

 ' notochord.' One end of the inclosed cavity dilates to 

 form the head (fig. 12 B), the other remains narrow, and 

 eventually becomes the tail ; the side walls of the body 



