266 Ross Granville Harrison 



and the sections are almost impossible to interpret. The descrip- 

 tion will therefore be confined to the other pair. While these 

 limbs are further advanced in development than those in the pre- 

 vious experiment, it was apparent from the observation of the 

 living specimen that they were not so well formed. They had a 

 slightly atrophic appearance and wxre never seen to undergo even 

 the slight twitching movements observed in the first experiment. 



Sections show that a small nerve trunk, which arises from the 

 eighth spinal nerve of the host enters the stalk which connects 

 the limbs with the abdominal wall, and running between the two 

 pelvic cartilages, is continued into the accessory or super-regener- 

 ated limb. This is all the more remarkable because no nerves 

 could be traced into the primary limb. The nerve in the accessory 

 leg follows the course normally taken by the n. ischiadicus. Above 

 the knee joint it divides into two trunks, one running to the flexor 

 and one to the extensor surface of the shank. Both of these are 

 cutaneous nerves and correspond respectively in distribution to 

 the r. cutaneus cruris posterior, w^hich arises normally from the 

 n. tibialis, and to the r. cutaneus cruris lateralis derived normally 

 from the n. peroneus. No muscular nerves can be made out below 

 the knee. 



The imperfect innervation ot the limbs in this case as compared 

 with the previous one is due no doubt to less firm implantation into 

 the tissues of the host. 



Experiment 1 11.^'^ In this case a hind limb bud taken from a 

 normal larva (Bufo lentiginosus) was implanted in the left side and 

 one taken from a nerveless larva on the right. The spinal cord 

 of the latter had been excised one week before. 



Both limbs developed well and produced accessory limbs. The 

 normal bud on the left produced a typical limb scarcely distinguish- 

 able from the primary. The nerveless limb produced an imper- 

 fect appendage, which in turn bore an accessory bud. The speci- 

 men was preserved forty days after the operation (Fig. 5). 



The limbs derived from the normal transplanted bud receive 

 a large nerve from the seventh spinal nerve of the host. Two 



'^Record number, Tr. Ext. 12. 



