TRANSACTIONS OF SECTION D. 13 
gave rise to the higher sub-grade, the Celomata, or animals with a cceelom or 
body-cavity surrounding the digestive tract. This latter includes all the remain- 
ing species of animals in nine Phyla, five of which are found fossil—the Echino- 
derma, Gephyrea, Mollusca, Appendiculata, and Vertebrata. 
Before proceeding further, I wish to lay emphasis on the immense evolutionary 
history which must have been passed through before the ancestor of one of the 
higher of these nine Phyla came into being. Let us consider one or two examples, 
since the establishment of this position is of the utmost importance for our argu- 
ment. First, consider the past history of the Vertebrata,—of the common ancestor 
of our Balanoglossus, Tunicates, Amphioxus, Lampreys, Fishes, Dipnoi, Amphibia, 
Reptiles, Birds, and Mammals. Although zoologists differ very widely in their 
opinions as to the affinities of this ancestral form, they all agree in maintaining 
that it did not arise direct from the Nematophora in the lower sub-grade of 
Metazoa, but that it was the product of a long history within the Coelomate sub- 
rade. The question as to which of the other Coslomate Phyla it was associated 
with will form the subject of one of our discussions at this meeting; and I will 
therefore say no more upon this period of its evolution, except to point out that 
the very question itself, ‘the ancestry of Vertebrates, only means a_ rela- 
tively small part of the evolutionary history of the Vertebrate ancestor within 
the Coelomate group. For when we have decided the question of the other 
Ceelomate Phylum or Phyla to whick the ancestral Vertebrate belonged, there 
remains of course the history of that Phylum or those Phyla earlier than the point 
at which the Vertebrate diverged, right back to the origin of the Ccelomata; while, 
beyond and kelow, the wide gulf between this and the Ccelentera had to be 
crossed, and then, probably after a long history as a Coelenterate, the widest and 
most significant of all the morphological intervals—that between the lowest 
Metazoon and the highest Protozoon—was traversed. But this was by no means 
all. There remains the history within the higher Protozoan sub-grade, in the 
interval from this to the lower, and within the lower sub-grade itself, until we 
finally retrace our steps to the lowest and simplest forms. It is impossible to 
suppose that all this history of change can have been otherwise than immensely 
prolonged ; for it will be shown below that all the available evidence warrants the 
belief that the changes during these earlier phases were at least as slow as 
those which occurred later. 
If we take the history of another of the higher Phyla, the Appendiculata, we 
find that the evidence points in the same direction. The common ancestor of our 
Rotifera, earthworms, leeches, Peripatus, centipedes, insects, Crustacea, spiders 
and scorpions, and forms allied to all these, is generally admitted to have been 
Cheetopod-like, and probably arose in relation to the beginnings of certain other 
Ceelomata Phyla, such as the Gephyrea and perhaps Mollusca. At the origin of 
the Coelomate sub-grade the common ancestor of all Coelomate Phyla is reached, 
and its evolution has been already traced in the case of the Vertebrata. 
What is likely to be the relation between the time required for the evolution 
of the ancestor of a Coelomate Phylum and that required for the evolution, which 
subsequently occurred, within the Phylum itself? The only indication of an 
answer to this question is to be found in a study of the rate of evolution in the 
lower parts of the animal kingdom as compared with that in the higher. Con- 
trary, perhaps, to anticipation, we find that all the evidences of rapid evolution are 
confined to the most advanced of the smaller groups within the highest Phyla, 
and especially to the higher Classes of the Vertebrata. Such evidence as we have 
strongly indicates the most remarkable persistence of the lower animal types. Thus 
in the Class Imperforata of the Reticularia (Foraminifera) one of our existing 
genera (Saccamina) occurs in the Carboniferous strata, another (Trochammina) in 
the Permian, while a single new genus (Receptaculites) occurs in the Silurian and 
Devonian. The evidence from the Class Perforata is much stronger, the exist- 
ing genera Nodosaria, Dentalina, Textularia, Grammostomum, Valvulina, and 
Nummulina all occurring in the Carboniferous, together with the new genera 
Archeediscus (?) and Fusulina. 
I omit reference to the much-disputed Eozoon from the Laurentian rocks far 
