28 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



syndactyly and leg-feathering (or " ptilopody "), at first sight apparently 

 distinct and uiu'elated, are in reality the prodnct of a single gene or a 

 single combination of genes. J. A. T. 



Transplanting Limbs of Amblystoma Embryo. — S. R. Detwiler 

 {Jouni. Exper. ZooL, 1920, 31, 117-69, 2 pis.). When the anterior 

 limb is excised and re-implanted to the same embryo at distances ranging 

 from 1-7 segments posterior to the normal position, there is a corre- 

 sponding decrease in the function of these limbs as they are implanted 

 more and more remote from the normal situation. Shifting the limb 

 does not effect a corresponding shifting of the segmental nerve contribu- 

 tion. If the limbs be so far posterior to the normal situation that thej 

 receive no innervation from the normal limb level of the cord, they 

 receive their main innervation from segments anterior to the transplanted 

 limb rather than from segments corresponding to the position of the 

 limb. The gradual decrease of function seems to be correlated with the 

 segmental nerve supply ; the function beisig more perfect when the 

 innervation is from the limb level. As the distance from the normal 

 increases the time required for initial limb reflexes increases, [t looks 

 as if the transplanted limb rudiment had a guiding influence on the 

 nerve contribution. The positive reaction toward this influence appears 

 to be greater in the nerves coming from the normal limb level of the 

 cord. The architecture of the nerve distribution within the transplanted 

 limb is the same as that in the normal limb. Gradually increasing the 

 distance Itetween the normal position and the transplanted limb brings 

 about a gradual increase in the number of reduplicated appendages. 

 The reduplication is manifestly non-adaptive. J. A. T. 



Transplanted Limbs and their Innervation.— 8. R. Detwiler 



{Froc. Nat. Acad Sci., 191!), 5, :'>24-P)l, 2 figs.). Additional limbs 

 transplanted ;!-5 segments posterior to the normal intact limb of the 

 Amblystoma embryo never attain the completeness of function attained 

 by limbs in the same relative position with the normal limb extirpated. 

 Although such limbs may. be well supplied with peripheral nerves, derived 

 from segments of the cord posterior to the normal limb level, their 

 greatly impaired movements appear to be a consequence of their 

 inadequate supply of central efl'erent neurones, which run apparently 

 only as far as the normal limb level, where they discharge into the 

 somatic motor centres of the normal intact limb. The generally 

 restricted and non-adaptive movements which these limbs do exhil)it 

 upon stimulation are probably effected through more or less imperfectly 

 connected intraspinal, intersegmental correlation neurones of the levels 

 from which peripheral innervation is derived. J. A. T. 



Regeneration of Fore-Brain in Amblystoma Larvae. — H. Saxton 

 BVRR (Joimi. Comp. Neurology, 191G, 26, 203-11, 4 figs.). Experi- 

 ments show that the fore-brain of Amblystoma larviv will not regenerate 

 when it and its functional end-organ are completely extirpated. The 

 healing of the wound results in the formation of a curtain across the 

 interventricular foramen derived from the ependyraa lining the neural 



