THE PLACOID BRAIN. 145 



the other require, in rowing, a cast of the rudder to keep them 

 straight in their course. 



Sinking altogether, however, the final cause of the pecu- 

 liarity, and regarding it simply as 2. foetal one, that indicates 

 a certain stage of imperfection in the creature in which it 

 occurs, on what principle, I ask, are we to infer that what is 

 a sign of immaturity in the young of one set of animals, is a 

 mark of inferior organization in the adult forms of another 

 set ? The want of eyes in any of the animal families, or the 

 want of organs of progression, or a fixed and sedentary con- 

 dition, like that of the oyster, are all marks of great infe- 

 riority. And yet, if we admit the principle, that what are 

 evidences of immaturity in the young members of one family 

 are signs of inferior organization in the fully-grown members 

 of another, it could easily be shown that eyes and legs are 

 defects, and that the unmoving oyster stands higher in the 

 scale than the ever-restless fish or bird. The immature Tii- 

 hularia possess locomotive powers, whereas in their fully de- 

 veloped state they remain fixed to one spot in their convoluted 

 tubes. The immature Lepas is furnished with members well 

 adapted for swimming, and with which it swims freely ; as it 

 rises towards maturity, these become blighted and weak ; and, 

 when fully grown, — fixed by its fleshy pedicle to the rock or 

 floating log to which it attached itself in its transition state, 

 — it is no longer able to swim. The immature Balanus is 

 furnished with two eyes : in its state of maturity these are 

 extinguished, and it passes its period of full development in 

 darkness. Further, it is not generally held that in the human 

 family a white skin is a decided mark of degradation, but 

 rather the reverse ; and yet nothing can be more certain than 

 that the negro foetus has a white skin. Since eyes, and or- 

 gans of progression, and a power of moving freely, and a white 

 skin, are mere embryonic peculiarities in the BalanuSy the 

 LepaSi the Tubidaria, and the negro, and yet are in themselves, 



