700 
ZOOLOGY: S. R. DETWILER 
Proc. N. a. S. 
sembled blotting paper models of the component parts of both fourth and 
eighth nerves, the former of which is in connection with the limb. Both 
motor and sensory roots of the fourth nerve (transplanted eighth) have 
undergone striking enlargement under the conditions which normally 
produce the increased proliferation of those centres in the limb region. 
The hyperplastic development of the sensory centres, secondarily brought 
into connection with a transplanted limb, has been shown in recent ex- 
periments,^ although no over-production of motor cells could be found. 
Under the conditions of the present experiments the nerve cells in the 
transplanted portion of the cord, which has been subjected to the factors 
normally producing the brachial enlargement, have undergone a degree 
of development, as indicated by a cell count, which almost equals that of 
the normal (table 3A, 1 and 2). The hyperplasia of the motor cells, 
however, under these conditions is evidently not the result of the func- 
tional activity of the limb with which the nerve is connected, for in the 
absence of the limb the production of cells in the limb level of the spinal 
cord is almost as great as under normal conditions (table 3A, 1 and 3). 
The possibility that the ingrowth of the axones of a given number of 
peripheral afferent neurones might determine the extent to which the 
motor centres will develop, is negated by the facts obtained from previous 
limb experiments,^ which show that a certain degree of both hypoplastic 
and hyperplastic development of the sensory neurones in a given reflex 
pathway can be induced experimentally without effecting a corresponding 
measure of development on the motor side. 
The evidence thus far obtained indicates, therefore, that the factor 
which is involved in the over-production of the motor cells is the stimulus 
afforded by the connection with the central neurones (bulbo-spinal fibers), 
a large number of which very likely run only as far as the limb level where 
they discharge into the appendicular motor centres. 
This preliminary report will be followed by a detailed account of the 
experiments, as well as a discussion of the results bearing more particu- 
larly upon the factors involved in the growth phase of nervous develop- 
ment. 
1 Detwiler, S. R., (a) These Proceedings, 5, 1919 (324-331); (b) Ibid., 6, 1920 
(96-101); (c) /. Exp. ZooL, 31, 1920 (117-169). 
2 See 1 (c) pp. 142-147, series AS5 and AS6. 
2 An account of healing and regeneration of the spinal cord in frog embryos is given, 
by Hooker, D., in the following papers: (a) J. Comp. Neur., 25, 1915 (469-495); (6) 
27, 1917 (421-449). 
4 Herrick, C. J., and Coghill, G. K., "The Development of Reflex Mechanisms in 
Amblystoma," /. Comp. Neur., 25, 1915 (65-85). 
5 See 1 (b). 
6 See 1 (5), pp. 96-98. 
