162 
PROFESSOR A. M. PATERSON ON THE DEVELOPMENT OP 
the j^oungest of my embryos, in which I have detected these, it has not been possible 
for me either definitely to determine the antero-posterior limits of the system, or to 
make certain whether the terminal masses of cells which form the ganglia are con¬ 
nected by a longitudinal commissure.” There is here only one positive observation, 
namely the connexion of the ganglia with the spinal nerves, which might be obtained 
from an examination of the adult, and Balfour himself, while inferring that the 
ganglia spring from the spinal nerves, and therefore from ectoderm, admits that his 
investigations, “ though they may naturally be interj)reted in this way, do not 
definitely exclude a completely different method of development for the sympathetic 
system.” In his ‘ Comparative Embryology ’ he states that “ the sympathetic 
ganglia (in Elasmobranchs) are at first simply swellings on the main branches of the 
spinal nerves, some way below the ganglia. ... I have been unable to find a longi¬ 
tudinal commissure connecting them in their early stages, and I presume they are at 
first independent, and become subsequently united into a continuous cord on each 
side.” He also derives the suprarenal bodies of Elasmobranchs from the sympathetic. 
Other observers, Brunn (16), Kolliker (17) and Braun (18), have shown that the 
medullary parts of the suprarenals are derived from the sympathetic, the cortical parts 
from undifferentiated mesoderm. 
ScHENCK and Birdsell (14), working with Chick, Dog, and Human embryos, 
came to the conclusion that the ganglia are derivatives of the central nervous system, 
and are pushed out from the spinal ganglia. Their paper is not, however, convincing; 
the illustrations do not clearly express the meaning of the text ; and the facts adduced 
do not appear to justify the generalisations at which they arrive. 
Onodi (15) has given the most complete account of the development of the sympa- 
tlietic. His researches cover all the classes of vertebrates. In fishes he studied the 
question in Scjjlliuni canicula, Miistelus Idivis, Scymnus, and Torpedo. In the first 
only he describes the earliest appearance of the sympathetic ganglia, as thickenings on 
the ventral ends of the spinal ganglia. These thickenings are comjaosed of large cells, 
w'hich stain deeply, are arranged in rows, and are sharply marked off from the pale 
mesoderm cells. By the further growth of this bulbous expansion the sympathetic 
ganglion is formed, remaining in connexion with the spinal nerve by a double row of 
cells. In the other examples, the commencement of the gangliated cord was not 
discovered ; in the youngest specimens examined the ganglia were fully formed, and 
connected to the spinal nerves (as Balfour described) by Rami communicantes. 
These rarni Onodi describes as being first cellular, afterwards becoming fibrous. The 
main conclusion of his researches in Fishes agrees with that of Balfour, that the 
ganglia are segmental and ectodermal in origin. They disagree, however, in regard 
to the jn-ocess of formation. Balfour regards the sympathetic ganglia as buds from 
the sjiinal nerves, the connecting stalk being gradually elongated into the ramus com- 
municans as the ganglion grows. Onodi, on the other hand, asserts that ganglia 
