McCrady.] 186 [Dec. 3, 



but a provisional group, very similar in character to that popular 

 classification by which all low forms of animal life are included to- 

 gether as worms or vermin. 



Before associating all vermiform animals together, in a single 

 group, we ought to recollect how great an obscurer of typical charac- 

 ter is Parasitism; Mimicry being an extreme illustration. 



Parasitism is indeed the universal condition of all finite being. 

 All animals and plants known to us are parasites of the earth; but 

 many are, besides, close parasites of other animals and plants, and 

 all animals and plants are,, in the large sense, parasites of other ani- 

 mals and plants. Sexual union should be regarded as a form of 

 temporary parasitism, marriage as a permanent form of parasitism. 

 Many organic forms also live attached to other bodies, whether or- 

 ganic or inorganic ; others live beneath the earth in caves, or in the 

 soil, mud, rock, or wet sand, as burrowers, either freely, oran struc- 

 tures formed by their bodies for protection; all these, though forms of 

 parasitism upon the earth, are very different from those other forms 

 of parasitism upon the earth, in which the animal moves freely upon 

 or above the surface of the ground, either through air or water. We 

 find, moreover, that when an animal has, at one period of its exist- 

 ence, habits of parasitism very different from those affected by its 

 nearest allies, that then it differs more or less from the morphological 

 norm of its nearest allies during the same period. The young Star- 

 fish, which enjoys a free existence in the sea, as a wandering geo- 

 parasite, during its larval stage, develops the complex and remarkable 

 structure of Brachiolaria or Bipinnaria; while other, and even closely 

 allied species, which pass the same period, as parasites upon their 

 mother, or attached to foreign bodies, develop nothing but obscure 

 rudiments of this Brachiolarian organism; and pass more or less di- 

 rectly into the form of the starfish. The subject itself is capable of 

 cosmical development. In the Animal Kingdom many other exam- 

 ples might be adduced, did space permit; among them I may notice 

 the peculiar structures developed by young placental Mammalia, in 

 consequence of their parasitism upon the womb of the mother; as 

 well as the corresponding structures developed by the mother in con- 

 sequence of the same parasitism, which otherwise sometimes leaves 

 impressions of a permanent character upon her organization, so that 

 all her offspring are apt to resemble the first born. These structures 

 developed by the female mammal are strictly comparable as effects of 

 parasitism to the galls developed in plants, in consequence of the 



