TRANSPLANTATION OF LIMBS IN AMBLYSTOMA 159 
The increase in the number of sensory neurones was deter- 
mined by counting the number of cell bodies in the spinal ganglia. 
Attempts to count the anterior horn cells were not successful, 
inasmuch as the anterior horn areas are not well differentiated 
at the age in which the larvae were studied and no accurate 
differentiation could be made between the anterior horn cells 
and the non-nervous cells (spongioblasts). The question dealing 
specifically with the effect of continued function of the limb 
upon the development of peripheral neurones, both afferent and 
efferent, will be discussed more fully in a later publication. How- 
ever, from a complete survey of the peripheral innervation, both 
from the standpoint of the number of muscles innervated and 
the amount of nerve contribution, it is highly improbable that 
the defective peripheral innervation can account for the great 
degree of imperfect movements that are exhibited by limbs in 
the series AS5 and AS6. | 
The remaining factor, therefore, viz., defective connections 
within the central nervous system, appears to be the only one 
which will adequately account for the marked deficiency of func- 
tion in limbs transplanted so far posteriorly as to be beyond 
the point where they will receive peripheral innervation from 
all or only a portion of the normal limb level of the cord. 
Although in normal larvae of this age the most obvious motor 
responses to various types of peripheral stimulation consists of 
total swimming reactions, under certain controlled conditions 
motor responses may be almost entirely limited to codrdinated 
movements of the limb. Such responses may be carried out 
perfectly by the transplanted limbs when their peripheral in- 
nervation is derived from the normal limb level of the cord, but 
the ability to exhibit movements codrdinated with those of the 
opposite intact limb decreases markedly when their peripheral 
innervation is derived from segments well beyond the normal 
limb level (series AS6). 
As has been shown by Herrick (’14), we have here a central 
nervous architecture by means of which peripheral sensory stim- 
uli pass through more or less localized ascending sensory tracts 
from the cord to the medulla (tractus spinobulbaris), to the mid- 
