12 



attaches itself permanently, head first to a rock ; its tail is 

 gradually absorbed, and with it the notochord disappears, while 

 the nervous system dwindle down to a solitary ganglion between 

 the mouth and the atrium, which distributes branches to the other 

 parts of the system, and cannot, even by courtesy, be called a 

 brain. Further than that, the outer coat actually becomes of a 

 vegetable nature, developing cellulose, a special characteristic of 

 plant tissues. (Stages shown by the diagrams). We have, repre- 

 sented here, as it might be, the life history of a man, born with all 

 the advantages of birth, riches, and refining associations, losing 

 them one after another, and, withdrawing from society with all its 

 civilizing influences, becoming at last the companion of savages, — 

 himself a savage. 



Of course one would not hastily conclude that all animals which 

 pass a free existence at first, and then become fixed are degraded 

 forms. The main point that decides it is the early possession of 

 organs belonging to higher creatiures, and the ultimate and inevit- 

 able loss of them. 



My second illustration is that of the Barnacle (Lepas anatifera) 

 found so frequently attached by long semi-animal stalks to floating 

 masses of wood. Who by the mere study of its ordinary form 

 would set it down as a near relation of crabs, lobsters, and shrimps ? 

 What has it in common with them ? What grounds have we for 

 classing it as a Crustacean, instead of a Mollusc, as former 

 zoologists did ? Only its early history, only the curious character 

 of its development. It begins life in a form only just below that 

 of a crab, and similiar to that of a cyclops, or a water flea, both of 

 which pass it by in development. Let me direct your attention for 

 a moment to these curious larval forms of Crustaceans. We have 

 here represented those of the Cyclops, a Shrimp [Pejiceus], the 

 Barnacle, and a Sacculina, which latter as we shall presently see, 

 is still more degraded than the barnacle. They are all well pro- 

 vided with organs of locomotion, and spend a very active youth. 

 So utterly unlike the parent form are they that they were long 

 regarded as distinct creatures, and were known by the generic 

 name Nauplius, which they still retain. The Shrimp and the 

 Cyclops pass through higher and higher stages, losing none of their 

 earlier advantages, and gaining many additional ones. But this 

 Barnacle Nauplius, not the least graceful of them all, after several 

 moultings like those of a caterpillar, during which it loses its 

 mouth, and then occupies its time as a bivolve, seeking a suitable 

 spot on which to vegetate, attaches itself firsL by a sucker and at 

 last by its head (diagram) to a block of wood with cement of its 

 own manufacture, loses its highly organized compound eyes, being 

 completely sightless for the rest of its life, and changes six pairs 



