284 THE ZOOLOGIST. 
those whose eggs, breaking up into cells, gave rise from those 
cells to distinct tissues. For the former he retained the old name 
of Protozoa, or first animals; for the latter he accepted and 
endorsed the Haeckelian term of Metozoa, or animals that came 
after the Protozoa. Using less objective terms, Maupas has 
recently suggested that we should speak of Cytozoa, or cell- 
animals, and Histozoa, or tissued animals. The change, however, 
is not needed, and, as I hope to show you, we are on the eve of 
changes enough. 
If you have gone with me so far you will have seen that the 
case against the Vertebrata and Invertebrata as representing the 
two prime divisions of the Animal Kingdom is now complete; 
allow me so far to comfort you as to assure that neither Cuvier, 
the father of comparative anatomy, nor von Baer, the father of 
embryology, ever accepted or endorsed this classification. 
I must beg to offer you what consolation I have at my 
disposal, for I am now going to ask you to go a step further, and 
to give up altogether, on the pain of losing your characters as 
well-informed zoologists, the appellations of Vertebrata and In- 
vertebrata ! 
I will first of all remind you of the history of the facts of the 
case, and will do so because you cannot hope to form a judgment 
on this subject, any more than on any which is of political 
interest, unless first of all you are led step by step through the 
processes by which opinion became formed. 
In 1864 Prof. Huxley published a classification of animals, 
which he would now be the first to call antiquated; in this there 
was a division of Mollusca-like animals (Molluscoida), one of the 
three groups of which was that of the Ascidians. In 1867 the 
distinguished Russian embryologist Kowalevsky published an 
account of his investigations into the early history of the mode of 
formation of the organs of the Ascidian body, which resulted in 
spanning the gulf between Vertebrates and Invertebrates in an alto- 
gether unexpected manner. Kowalevsky showed that in Ascidians, 
just as in ‘ Vertebrates,’ the central nervous system arises by 
the formation of a dorsal groove, the sides of which gradually 
closed over, met and formed a dorsal neural tube, whereas 
in other high ‘Invertebrates’ the central nervous system arises 
as a solid thickening of the ventral middle line, which gradually 
sinks away from the surface, but is never hollow, and never folded — 
