TRANSACTIONS OF SECTION D. 4.4.3 
FRIDAY, SEPTEMBER 1. 
The following Papers were read :— 
1. Convergent Evolution, as illustrated by the Litopterna, a Group of 
Fossil Ungulata in Patagonia. By Professor W. B. Scorv. 
While Convergent Evolution is admitted by most naturalists to be a frequent 
and important phenomenon, there is a great difference of opinion as to how nearly 
identical the results of such a mode of development might be. So far as the 
Litopterna are concerned, there are striking resemblances to certain Perissodactyls 
in teeth, skull, and skeleton, but the differences are many and fundamental. It 
does not appear at all likely that so complex a structure as a mammalian skeleton 
was ever produced in identical terms by two independent series. 
2. A Neuro-syncytial Theory of Development. 
By Dr. W. H. Gaskett, FBS. 
The author referred to his theory of the origin of Vertebrates, and pointed out 
that it was based upon the paramount importance of the central nervous system as 
the chief factor in the upward progress of the animal kingdom. Every line of 
investigation pointed to the conclusion that the vertebrate arose from that group 
of invertebrates which possessed a central nervous system most nearly similar to 
that of a low vertebrate, such as Ammocotes—an invertebrate, therefore, belonging 
to the group of Arthropods. This argument had been worked out by the author 
in a series of papers published in the ‘ Journal of Anatomy and Physiology,’ and 
receives especial support from the paleuntological record. For the dominant race 
now, the biped mammal man, arcse undoubtedly from the highest race evolved up 
to that time, the quadrupedal mammals; these in their turn originated from the 
dominant reptiles, these again from the amphibians, which were the most highly 
organised group at the time. The amphibians themselves came from the dominant 
race living in the sea at the time, the fishes; and so, too, according to the author’s 
theory, the fishes arose directly out of the race dominant at the time, 2.c., the 
arthropod group. This theory necessitates the formation of a new alimentary 
canal at the transition from the arthropod to the vertebrate; a requirement which 
is no more unlikely than the formation of a new respiratory apparatus at the tran- 
sition of a fish into an amphibian. The reason why others have found this forma- 
tion of a new alimentary canal so difficult of acceptance is because embryology, 
and embryology alone, in its recent teaching makes the alimentary canal, and not 
the central nervous system, the important organ around which an animal is built 
up. The author, basing himself especially on Braem’s papers in the ‘ Biologisches 
Centralblatt,’ pointed out that in reality the germinal-layer theory was a physio- 
logical and not a morphological conception ; that the one criterion of hypoblast was, 
not its mode of formation, but its ultimate fate, whether or no the detinite alimen- 
tary canal was formed from it. Morphological laws of development must exist, 
but, to quote Samassa, ‘ one thing can be said with certainty at the present time: 
the germinal-layer theory is not one of them,’ The author suggested a reconsidera- 
tion of the whole matter, and starting with the adult pointed out that the tissues 
of the body fall naturally into two great groups: those which are connected with 
the central nervous system—the master tissues of the body—and those which live 
a free existence without any such connection. The body may be looked upon as 
composed of a neuro-epithelial syncytium in the meshes of which free cells live. 
The author then considered the evidence for such a neuro-epithelial syncytium, 
and showed how a one-layered blastula must result from the coming together ot 
the neural and epithelial moieties as we pass from the adult to the embryo. He 
then discussed the nature of the second group of cells, those not connected with 
the central nervous system, and suggested that they owe their origin to the germ 
cells, This led to the further suggestion that the Metazoa arose from the Protozoa 
