298 LEIGH HOADLEY. 



of the forebrain, and secondly, that the nasal pit is capable of 

 independent differentiation. Both sets of experiments were done 

 with the larva of Amblystoma. In the first type of experiment, 

 though the forebrain primorditmi was removed, the nasal epi- 

 thelium sent out nerve processes into the adjacent mesenchyme, 

 developing normally. The second type of experiment involve the 

 transplantation of the excised nasal pits to a position beneath the 

 ectoderm dorsal to the eye. Lewis (page 464) states that 

 ". . . differentiation of the organ continued and nerve fibers 

 were sent off into the region between it and the ectoderm, . . . 

 but extend only a short distance." 



In the grafts obtained from the transplantation of the nasal 

 region of the chick embryo, the different parts of the organ show 

 a high degree of specificity in the course of their differentiation. 

 In comparing them with the control and with the description of 

 the process of nerve formation by Disse, it was found that they 

 show a condition comparable to growth in a normal embryo of the 

 same age. The cartilage which is present, is, without a doubt, 

 that of the transplanted part, and not of the host. The nasal 

 sacs are present in nearly their normal relationships to the rest 

 of the parts and have a differentiation closely resembling that of 

 the same parts in the normal organ. The nasal epithelium gives 

 rise to the nerve which is also present. The nerve cells of the 

 forebrain differentiate nerve processes, the abnormal appearance 

 in the sections being due to excessive vascularization and the 

 absence of the limiting membrane, both of which are mechanical 

 factors controlling the limits of differentiation to a great degree. 



C. The Otic Region. 



Grafts of the otic region and the otic vesicle are much more 

 difficult to make than those of the nasal region. The auditory 

 pit appears about the thirty-six hour stage, and the vesicle is 

 closed about the forty-eight hour stage; the material grafted 

 was taken from embryos of the last mentioned age in most cases. 

 The first experiments were made by shelling out the otocyst and 

 transplanting it, but it appeared very soon that the oto< \ -t .ilone 

 does not persist well in grafts. The mechanical injury due to the 

 pressure of the egg itself, together with the adhesive quality of 



