HELMINTHA. O 



Their bathymetric position or distribution in heiglit and depth in 

 relation to our planet, will likewise accord with that of the 

 infested animals ; so that, in short, the length, breadth, and 

 area of their geological and geographical range will be identical 

 with that of the vertebrate groups whose individual bodies they 

 inhabit. 



The truth of this general proposition, taken merely as an 

 hypothesis, can scarcely be assailed ; yet, I have not omitted 

 to seek diligently for practical evidence of the existence of internal 

 parasites in ancient times. This I have done by scraping down 

 portions of fossil excrement, submitting the same to microscopic 

 observation, in the hope of stumbhng upon a parasite's hook or 

 spine. Of course a search of this kind could scarcely be ex- 

 pected to prove effective, because the dehcate structure of the 

 entozoa, the minuteness of their bulk, and, more particularly, the 

 extreme rarity of their being mixed with the eliminated contents of 

 the alimentary canal, at once suggest almost insuperable barriers 

 in the way of success. I do not yet despair, however, of 

 recording ocular proof of the occurrence of entozoa in the 

 secondary and tertiary epochs. 



For the reasons already stated, it is not my intention to break 

 up the helminths into separate animal groups, but to retain them 

 as a single class, forming the lowermost section of the articulate 

 division of the animal kingdom. Certainly the majority of the 

 helminths conform to the annulose type, and I cannot but regard 

 those views as fanciful which would place the Cestodes among 

 the Radiaria ; especially, since this idea is based chiefly on the 

 radiated character of the so-called tapeworm head. At all events, 

 every attempt to distribute the entozoa amongst the different 

 invertebrate groups to winch they are supposed to be most 

 closely aUied, has hitherto been attended with endless confusion ; 

 therefore, in the present state of our knowledge, it is manifestly 

 prudent to continue the method actually thrust upon us by 

 experience. In this view I off'er the following scheme of classifi- 



