236 THE COMING OF AGE OF vii 



links of. connection between the two ; but the 

 investigations of Kowalewsky and others upon 

 the development of Amphioxus and of the Tunicata, 

 prove, beyond a doubt, that the differences which 

 were supposed to constitute a barrier between 

 the two are non-existent. There is no longer any 

 difficulty in understanding how the vertebrate 

 type may have arisen from the invertebrate, 

 though the full proof of the manner in which 

 the transition was actually effected may still be 

 lacking. 



Again, in 1859, there appeared to be a no less 

 sharp separation between the two great groups of 

 flowering and flowerless plants. It is only subse- 

 quently that the series of remarkable investiga- 

 tions inaugurated by Hofmeister has brought to 

 light the extraordinary and altogether unexpected 

 modifications of the reproductive apparatus in the 

 Lycopodiacece, the Rhizocarpcce, and the Gymno- 

 spermece, by which the ferns and the mosses are 

 gradually connected with the Phanerogamic 

 division of the vegetable world. 



So, again, it is only since 1859 that we have 

 acquired that wealth of knowledge of the lowest 

 forms of life which demonstrates the futility of 

 any attempt to separate the lowest plants from 

 the lowest animals, and shows that the two king- 

 doms of living nature have a common borderland 

 which belongs to both, or to neither. 



Thus it will be observed that the whole ten- 



