318 THE COMING OF AGE OF [LECT. 



the region of hypothesis to that of demonstrable 

 fact. 



In 1859, there appeared to be a very sharp and 

 clear hiatus between vertebrated and invertebrated 

 animals, not only in their structure, but, what was 

 more important, in their development. I do not 

 think that we even yet know the precise 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 investigations 

 inaugurated by Hofmeister has brought to light the 

 extraordinary and altogether unexpected modifications 

 of the reproductive apparatus in the Lycopodiacece, the 

 Rhizocarpece, and the Gymnospermece, 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 ac- 

 quired 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. 



