12 JOURNAL OF THE [January, 



sitical animals, and the males of most rotifers, or wheel animal- 

 cules (which occupy a comparatively high position in the scale of 

 organization), have no digestive apparatus whatever, as far as can 

 be discovered, while the fresh-water hydras and many other lowly 

 animal forms receive their food as well at one point as at another, 

 and in fact perform the act of digestion throughout the whole 

 body. So Cuvier's and Ehrenberg's principal criteria of animality 

 have broken down and disappeared from the domain of biology, 

 and along with them have gone all the other old-time tests. Dar- 

 win's researches on insectivorous plants gave a fatal blow to the 

 theories built upon sensitiveness and response to stimuli, on the 

 power of complex motion directed to a definite end, and on the 

 appropriation and assimilation of organic food. , 



For a long time the existence of chlorophyll in an organism was 

 deemed conclusive evidence of its vegetable nature, for chloro- 

 phyll is what gives the green color to all the higher kinds of 

 plants, and chemistry had shown that chlorophyll was the seat of 

 those operations which separated the carbon from carbonic acid 

 and built it into the woody substance of the plant, and carbon 

 was regarded as belonging strictly to the vegetable world. But, 

 alas for consistency, it was found that some plants do not contain 

 chlorophyll, and, still worse, that there are certain undoubted 

 animals which are possessed of it and that in their economy it 

 performs the very same duty that it performs in plants. 



1 would not have it understood from all this that there is a bor- 

 der country into which organisms may wander from the animal 

 and the vegetable kingdoms and therein lose all definite character 

 and all trace of their origin ; or that, by crossing this no-man's 

 land, the former inhabitants of one domain may become thor- 

 oughly naturalized in the other. There is no such magic about 

 this curious region. Its perplexities and uncertainties mainly 

 grow out of the fact that it is the place where the frayed-out 

 edges of the two kingdoms come together to form a hazy mixture 

 of intermingled fringes. The ravelled threads have not necessa- 

 rily lost their identity, though we are unable to disentangle them. 

 While there are many living forms which at present cannot be 

 definitely classed with either animals or vegetables, experience 

 leads us to think that, in most cases, if we could trace out the 

 complete life-histories of the doubtful organisms occupying this 



