164 H. L, WIEMAN 



in the transplant, so that reactions and development due to its- 

 original polarity could be studied to best advantage. 



The operation was accomplished by two transverse incisions 

 through the neural tube and somites, followed by a longitudinal 

 cut on each side connecting the lower ends of the transverse 

 incisions and extending to the midhne in a frontal plane. In 

 some cases the notochord was purposely cut and moved with the 

 transplant; in other cases it was left intact. The piece thus 

 freed was lifted out, swung around through 90°, and pressed into 

 the wound. The purpose in removing somite with the neural 

 tube was to preserve as nearly as possible normal conditions for 

 any nerves that might later develop from the transplanted tube, 

 and, at the same time, to provide a non-nervous block between 

 the stumps of the neural tube and the transplant. The usual 

 practice was followed in holding the transpant in place by means 

 of thin glass rods bent to fit snugly over the embryo at the site 

 of operation. From five to fifteen minutes sufficed for the trans- 

 plant to become attached, after which the holders were removed. 

 After an hour or so in 0.4 per cent salt solution, in which also the 

 operations were performed, the embryos were removed to tap- 

 water and allowed to develop at a temperature of 15° to 20°C.^ 



Following the operation, the embryos were examined from time 

 to time under the binocular, sketched, and tested for nervous 

 conductivity through the transplant by means of delicate tactile 

 stimuli. The material was fixed in corrosive-acetic, embedded in 

 rubber-paraffin, cut into lOju sections, and stained on the slide. 

 On the whole, the most satisfactory staining results were obtained 

 with Delafield's haematoxylin and orange G. 



The stages most frequently used for operations reported on at 

 the present time are shown in figure 1, A and B; C and D are 

 outlines of older stages also used. The sketches were made 

 five minutes after the operation. These stages showed no 



1 During the spring of 1920, the author enjoyed the privilege of spending two 

 weeks at the Osborn Zoological Laboratory of Yale University, which afforded 

 opportunity to observe the operative technique as practiced and so highly per- 

 fected by Professor Harrison and his students. To Professor Harrison and the 

 zoological staff at Yale the writer begs to express his deep sense of appreciation 

 of the courtesy and privileges extended to him during his visit there. 



