154 GEORGE L. STREETER 



the vesicle should lie against the brain, and the median or convex 

 surface toward the opening of the wound. The lateral and median 

 surfaces of the vesicle are easily recognized and therefore this 

 transplantation in a reversed posture can be done with great 

 accuracy. This method of placing the vesicle has a double ad- 

 vantage. It furnishes a complete rotation of 180 degrees and it is 

 a secure way to transplant the vesicle which is very easily wedged 

 in the pocket in that posture. The vesicle shows no tendency to 

 escape, and as the lips of the wound are not very wide apart, it 

 is not necessary to take any precautions about holding them to- 

 gether. They take care of themselves and need no superimposed 

 weights or further attention. The specimen is now set aside 

 and in the course of three or four hours all traces of the wound 

 have disappeared. The specimens are allowed to go on with 

 their development for fourteen days, the period usually necessary 

 for the formation of the canals, at the end of which time they are 

 preserved in a chrome-acetic mixture and are ready for examina- 

 tion. In most of the operations two specimens were utilized, 

 one always being discarded after transplanting its right vesicle. 

 In four experiments the writer succeeded in making a complete 

 exchange of the right vesicle between the two specimens and pre- 

 serving both of them. This involves great care and the addition- 

 al effort required does not justify the procedure. The preserved 

 specimens were imbedded in paraffin, cut in series and stained 

 with hematoxyhn and congo-red. Examination of them showed 

 that nineteen of the experiments were successful, in that the 

 transplanted vesicle had continued in its development far enough 

 to recognize its different parts and their posture. Wax-plate 

 models after the Born method were made of them all, and draw- 

 ings of these, together with a photograph of a selected section 

 from each series, are shown in figures 1 to 38. I may here state 

 that these photographs were made with the apparatus belonging 

 to my colleague. Professor Novy, and it gives me pleasure to 

 take advantage of this opportunity to acknowledge his courtesy 

 and his assistance in their preparation. 



Other operations were performed with a view to the determina- 

 tion of character and degree of the environmental control, but these 



