1847.] Mternation of Generations, etc., 275 



change, they then attach themselves for a permanent hold. Their 

 first effort then, is to rid themselves of their tails, which they do 

 by frequent jerks, and being cast off, it then becomes a lifeless 

 particle. The Cercaria, as if to gain a better footing upon the 

 snail after casting off its appendage the tail, turns around again 

 and again, in order to bore itself deeper into the flesh. During 

 this time it throws off from its body an abundant mucous secretion 

 which is designed to form a case or covering which becomes 

 slightly indurated. Beneath this case which is considered analo- 

 gous to a pupa case, the animal remains in comparatively a quies- 

 cent state. The animal having encased itself as above stated, 

 and this is usually, if not always effected in autumn, remains till 

 about January. It now penetrates through the skin, and finally 

 into the liver of the snail. In its progress it loses its organiza- 

 tion in part, the rows of spires fall off, the viscera become ob- 

 scure, and it assvmies more and more the form of the fluke, more 

 liver-like in its condition, or more shapeless. It however pre- 

 serves its identity, it is an animal feeding upon the highly ani- 

 malized part, the liver, and here its ova for another brood are 

 formed and ejected, passing into the fluids, and then outwards, 

 assuming a state and condition which observation has not yet .de- 

 termined on. So probably every species of fluke, which inhabit 

 sheep and other higher grades of animal kind, appear in a peculiar 

 state, and under peculiar forms, before they are prepared to pene- 

 trate these highly animalized abodes, where though they are less 

 active or more sluggish, yet are evidently in a higher grade of 

 existence, than the one during which true ova are formed, and 

 from A\hich a numerous progeny of flukes will arise. 



We pass now to the concluding remarks of the author, though 

 we have by no means brought out one of his main ideas so full as 

 we ought, viz., that the sustenance of the individual destined to 

 become identical with the parent by the instrumentality of nurses, 

 the latter being the direct product of the mother, and which is 

 the generation so unlike its parent. But we shall state first an 

 interesting as M'ell as important doctrine, that so far as a complete 

 conception in our minds of a species is formed, it must take in 

 all the stages and forms in which they exist. An idea of a male 

 female parent is insufficient, so long as their unlike progeny is 

 unknown or left out. With this idea an individual cannot repre- 

 sent the species. This idea of a nursing progeny differs from 

 that involved in the common metamorphosis of the larva of a but- 

 terfly. 



Organism, analogy, and indeed observation to a certain extent go 

 to prove that the entozoa, intestinal worms, tape worms, flukes, 

 etc., all exist in an individual state out of the body, and never 



