575 i 
596 
~I 
A New Reading for the Annulate Ancestry of the 
Vertebrata 
HE question of the ancestry of the vertebrates being still 
unanswered, anyone is at liberty to make suggestions. No 
new facts seem to be forthcoming to enlighten us; we are driven 
therefore to find new readings of the old. To those who scorn all 
theorizing, and are content to wait until the new facts turn up, | 
would suggest the following questions: Are we sure we have read 
all that the old facts have to teach us? Have we arranged them 
in every possible order, and are we competent to deny that they 
ean yield us any clue to the solution of the problem ? 
I ask these questions somewhat feelingly, because I have 
recently lighted upon a new way of arranging the old facts, and 
I propose to offer it to my fellow-zoologists for what it is worth. 
This much, indeed, I claim for it, viz, that it shows a way of 
escaping from at least some of the difficulties in the way of the 
annulate origin of vertebrates. It provides us with another escape 
from having to assume that the annulate ancestor, with its ventral 
nerve-cord, turned over on to its back to become the vertebrate 
with its dorsal nerve-cord; and it shows how the notochord and 
neural plate, those most characteristic of all vertebrate structures, 
might have been unsegmented from the beginning as secondary 
developments within an originally seginented body. I propose, in 
short, to show how the assumption of a primitive hirudinean as our 
ancestral annulate enables us so to re-arrange the old facts as to bridge 
over the gulf between the invertebrates and vertebrates with start- 
ling ease. I do not affirm that our nearest invertebrate ancestor 
was a hirudinean. I only wish to show how it is conceivable that 
a primitive leech might have developed into a low vertebrate form 
allied to the cy clostomes. 
My attention was first directed to the hirudineans by the fact 
that the embryonic muscles of cyclostomes and sharks are of the 
same type as are the muscles of the leech. JI am well aware that 
histological resemblances are in themselves of no value to morphology. 
In this case the resemblance served to suggest the hirudineans as 
the possible annulate ancestors of the cyclostomes. As_ is 
well known, they, like the cyclostomes, have no appendages, no 
B 
