ANIMALS AND PLANTS. 185 



a gulp, into the pulpy central substance of the body, 

 there to circulate up one side and down the other, until 

 its contents are digested and assimilated. Neverthe- 

 less, this complex animal multiplies by division, as the 

 monad does, and, like the monad, undergoes conjuga- 

 tion. It stands in the same relation to Heteromita on 

 the animal side, as Coleochcete does on the plant side. 

 Start from either, and such an insensible series of gra- 

 dations leads to the monad that it is impossible to say 

 at any stage of the progress here the line between 

 the animal and the plant must be drawn. 



There is reason to think that certain organisms which 

 pass through a monad stage of existence, such as the 

 MyxomyceteS) are, at one time of their lives, dependent 

 upon external sources for their protein matter, or are 

 animals ; and, at another period, manufacture it, or are 

 plants. And seeing that the whole progress of modern 

 investigation is in favour of the doctrine of continuity, 

 it is a fair and probable speculation though only a 

 speculation that, as there are some plants which can 

 manufacture protein out of such apparently intractable 

 mineral matters as carbonic acid, water, nitrate of am- 

 monia, metallic and earthy salts ; while others need to 

 be supplied with their carbon and nitrogen in the some- 

 what less raw form of tartrate of ammonia and allied 

 compounds; so there may be yet others, as is possibly 

 the case with the true parasitic plants, which can only 

 manage to put together materials still better prepared 

 still more nearly approximated to protein until we 



