236 THE COMING OF AGE OF vir 
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 
Lycopodiacee, the Rhizocarpee, 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. — ‘7 
Thus it will be observed that the whole ve 
