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 ofa 
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 creatures, and the ultimate and inevit- 
able loss of them. 
My second illustration is that of the Barnacle (Zepas 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 lifein 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 
@ moment to these curious larval forms of Crustaceans. We have 
here represented those of the Cyclops, a Shrimp (Penaeus), 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 retam. 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 first 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 
