80 Dr Treviranus on the 



not yet been discovered, it is not improbable that they are an 

 attribute of all animals, even the lowest. It is quite otherwise 

 with plants. Their tissues are so transparent, that if a nervous 

 matter at all analogous to that of the nervous animals existed, it 

 would lon^: afjo have been observed. 



Here is, therefore, a negative character of plants ; and in 

 their classification some other system than the nervous must be 

 made the basis of division. Their positive character consists in 

 the composition of their whole internal substance of sohd cells 

 and unbranched vessels. Their cells are separated by intervals, 

 and are connected together in a reticulated form. These inter- 

 vals have no proper coats. Globules and not cells are the ele- 

 mentary parts of the animal tissues, and their vessels are al- 

 ways branched. When we approach the confines of the animal 

 and vegetable kingdoms, — whenever the vegetable tissues are 

 destitute of solid cells and of vessels, it is always difficult to de- 

 termine to which of the two kingdoms they ought to be referred, 

 from their want of the distinctive characters of the animal and 

 vegetable tissues. 



It might be supposed that the embryo, with its envelopes, 

 was the miniature expression, — the microcosm of the perfectly 

 developed animal, and that the complexity of each were directly 

 proportioned to each other, so that the degree of affinity between 

 organic existences might be concluded from the similarity of their 

 ova and embryos. The appreciation of these resemblances has 

 great or even insurmountable difficulties in animals, but is much 

 easier in plants. The characters deduced from the formation 

 of the embryo and its envelopes, have been found the fittest for 

 the natural arrangement of plants. They are the bases of the 

 Jussieuan System, which I must suppose to be well known to all. 



Rudolphi was the first who attempted to arrange animals ac- 

 cording to the structure of their nervous system*. He divided 

 them into those with, and those without, a visible nervous sys- 

 tem ; but such a division is of no value for biology. Our au- 

 thor has only given the most general distinctions of the classes 

 provided with a nervous system. I have also occupied myself 

 much with this subject ; but my contributions are still merely 

 fragments ; but I doubt not that a very splendid superstructure 



• Beitrage zur Anthropologic und Allgemeinen Naturgeschichte. 



