470 DAVENPORT HOOKER 
were brought into contact with one another and kept apposed 
until the skin cut had healed. By this means he found it possible 
to perform homo- and heteroplastic fusions of pieces of embryos. 
Harrison (’98, ’02) not only succeeded in fusing halves of embryos 
of different species, but carried such a composite embryo through 
its metamorphosis. Where careful apposition of the wound sur- 
faces is practiced, no active regenerative processes ensue. Under 
such circumstances the various organs heal per primam, the tis- 
sues fuse together and the embryos possess the normal con- 
tinuity of all their structures within a very short time after the 
operation. On the other hand, if the spinal cord be severed and 
its cut edges are not brought into contact with one another, a 
very definite series of events ensues which tends toward the 
reunion of the cord. The present paper deals with these regenera- 
tive processes and the gross points of the behavior of embryos 
operated in this manner. 5 
EXPERIMENTS 
Method. Embryos df Rana sylvatica, 3.5 to3.75 mm. in length, 
were operated upon in 0.4 per cent saline under a Zeiss binocular 
microscope. Anaesthesia was unnecessary as the peripheral 
nervous system has not as yet begun its development. With a - 
finely pointed pair of Noyes’ iridectomy scissors a cut'was made 
in the dorsal portion of the body just behind the small projections 
which mark ,the position of the pronephroi. Care was taken to 
cut completely the skin of the dorsal half of the embryo, the 
neural tube, the notochord and the myotomes on each side of 
the cord in such a manner that the two portions of the body were 
connected to one another only by the yolk and the skin of the 
ventral and ventro-lateral region. 
The physiological tests for interruption of the continuity of 
the spinal cord, so valuable in older stages, are not applicable 
here, as the embryos do not move. At the time of operation 
it is possible, however, to see the cord and notochord byslightly 
separating the edges of the cut and to observe the completeness 
of the operation so far as these structures are concerned. The 
