NATURAL SELECTION 



9 1 



limbs or swimmerets, no mouth and no anus. As Professor 

 Ray Lankester puts it, the creature is "a mere sac filled with 

 eggs, and absorbing nourishment from the juices of its host by 

 root-like processes." l Any of the many types of free-swimming 

 crustaceans would in such a situation be out of place. 



The barnacle is a familiar example of degradation. It too 

 begins life as a Nauplius swimming freely in the ocean. But on 

 attaining maturity it fixes itself by a long stalk to a ship's bottom 



FIG. 12. (From Ray Lankester's Degeneration.) (A) Nauplius of Sacculina, etc., (B) Sacculina. 



or to a pile. Its antennae disappear ; its antennales are found 

 imbedded in the stalk, revealing the fact that it has fixed itself 

 by its head ! The eyes and eye-stalks have vanished. Thus it 

 has shed or lost the use of all the delicate sense organs, and has 

 been well compared to " a man standing on his head and kicking 

 his food into his mouth." 2 The stalkless barnacles or "acorn- 

 shells" are familiar objects on rocks on the sea-shore. If they 

 are put in an aquarium they may be seen rythmically opening 

 their bivalved carapaces and protruding their limbs, like their 



Degeneration, p 34. 



Quoted by Prof. Lankester, Degeneration , p. 37. 



