126 ESSAY ON CLASSIFICATION 



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 

 Radiata there are no parasites, properly speaking; some of them 

 only attaching themselves by preference to certain plants, while the 

 young of others remain connected with their parent, as in all Corals, 

 and even among Crinoids, as in the Comatula of Charleston. 



In all these different cases the chances that physical agents may 

 have a share in producing 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 complicated circumstances of their 

 peculiar mode of existence and their various connections with other 

 animals. Now if it can already be shown from the mere connections 

 of independent animals that external circumstances 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 their final meta- 

 morphosis and in which this succession is normal? Was such an ar- 

 rangement 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, 



