^q8 H. S. Jennings 



while the spined animal is free. The spine is still at the anterior 

 tip; it has not moved backward for two generations. 



This individual did not divide for more than twenty-four hours, 

 and during its lifetime the spine became a little shorter. The 

 animal now used the spine almost continually. It placed the tip 

 of the spine against the bottom of the vessel or against any other 

 surface, then ran along the surface, keeping the tip of the spine 

 in contact, while currents of water passed down the oral groove 

 (Fig. 5). This use of the spine is of course incidental to the com- 

 mon habit of these animals, of placing one side of the body against 

 a surface and running along it. But this is the first generation in 



Fig. 5 Use of the spine by the individual of the twenty-first generation. The tip of the spine is 

 pressed against a surface and the animal runs along it, in the direction indicated by the large internal 

 arrow, while the currents of water down the oral groove to the mouth are indicated by the small arrows. 



which such a use of the appendage occurred. This, taken with 

 the fact that the appendage seemed to be gaining a permanent 

 position at the anterior tip suggested possible interesting develop- 

 ments in the future. 



Twenty-second generation. The spine again remained at the 

 anterior tip. The division (afternoon of May 18) was at first not 

 complete (Fig. 4, ^-), the animals remaining connected for more 

 than twenty-four hours. 



On the morning of May 20, the two had separated, but had not 

 divided farther. Both were swollen and opaque; they were evi- 



