TRANSACTIONS OF SECTION D. 21 
Discina) even generically identical. The demand for time to originate the group 
is quite as grasping as that of the others we have been considering. 
All the Classes of Echinoderma, except the Holothurians, which do not possess 
a structure favourable for fossilisation, are found early in the Paleozoic rocks, 
and many ofthem inthe Cambrian. Although these early forms are very different 
from those which succeeded them in the later geological periods, they do not possess 
a structure which can be recognised as in any way primitive or ancestral. The 
Echinoderma are the most distinct and separate of all the Colomate Phyla, 
and they were apparently equally distinct and separate at the beginning of the 
fossiliferous series. 
In concluding this imperfect attempt to deal with a very vast subject in a very 
short time, I will remind you that we were led to conclude that the evolution of 
the ancestor of each of the higher animal Phyla probably occupied a very long 
period, perhaps as long as that required for the evolution which subsequently 
occurred within the Phylum. But the consideration of the higher Phyla 
which occur fossil, except the Vertebrata, leads to the irresistible conclusion that 
the whole period in which the fossiliferous rocks were laid down must be 
multiplied several times for this later history alone.. The period thus obtained 
requires to be again increased, and perhaps doubled, for the earlier history. 
In the preparation of the latter part of this address I have largely consulted 
Zittel’s great work. I wish also to express my thanks to my friend Professor 
Lankester, whom I have consulted on many of the details, as well as the general plan 
which has been adopted. 
PRINTED BY 
SPOTTISWOODE AND CO., NEW-STREET SQUARE 
LONDON 
