126 ESSAY ON CLASSIFICATION. Part I. 



Among Mollusks, parasites are very few, if any can properly be called true 

 parasites, as the males of some Cephalopods living upon their own females;^ as the 

 Gasteropods growing buried in Corals,^ and the Lithodomus and a variety of Areas 

 found in Corals. Among Eadiata there are no parasites, properly speaking; some 

 of them only attaching themselves by preference to certaui plants, wliile the young 

 of others remain connected with their parent, as in all Corals, and even among 

 Crinoids, as in the Comatvda of Charleston. 



In all these different cases, the chances that physical agents may have a share 

 in producmg such animals are still less than in the cases of independent animals, 

 for here we have superadded to the very existence of these beings all the com- 

 phcated circumstances of their pecuhar mode of existence and their various con- 

 nections with other animals. Now, if it can already be shown from the mere 

 connections of independent animals, that external circmnstances cannot be the cause 

 of their existence, how much less could such an origin be ascribed to parasites! 

 It is true, they have been supposed to originate in the body of the animals upon 

 which they live. What then of those who enter the body of other animals at 

 a somewhat advanced stage of growth, as the Gordius? Is it a freak of his? 

 Or, what of those which only live upon other animals, such as lice ; are they the 

 product of the skin? Or, what of those which have to pass from the body of 

 a lower into that of a higher animal, to undergo then- final metamorphosis and 

 in which this succession is normal? Was such an arrangement devised by the first 

 animal, or imposed upon the first by the second, or devised by physical agents 

 for the two? Or, what of those in which the females only are parasites? Had 

 the two sexes a different origin? Did perhaps the males and females originate 

 in different ways ? 



I am at a loss to conceive how the origin of parasites can be ascribed to 

 physical causes, unless, indeed, animals themselves be considered as physical causes, 

 with reference to the parasites they nourish ; and if so, why can they not get 

 rid of them, as well as produce them, for it cannot be supposed, that all this 

 is not done consciously, when parasites bear such close structural relations to the 

 various types to which they belong? 



The existence of parasitic animals belonging to so many different types of the 

 animal as well as the vegetable kingdom, is a fact of deep meaning, which Man 

 himself cannot too earnestly consider, and, while he may marvel at the fact, take 

 it as a warning for himself, with reference to his boasted and yet legitimate inde- 



^ See above, p. 74, note 1, Kolliker, Muller, ^ Ruppell, (Ed.,) M(5inoire sur le Magilus 



Verany and Vogt, etc. antiquus. Trans. Soc. Strasb., 1832, 1., fig. 



