IOWA ACADEMY OF SCIENCES. 105 



cnloroform equal parts, pure chloroform, chloroform with a small per cent 

 of paraftine dissolved, iucreasing the percentage of paraffine frcm time to 

 time, using just heat enough to to keep the solution a liquid, "soft" melted 

 parafine, finally "hard" melted paraffine. The time required for the process 

 was sometimes two to three weeks, but with the younger tissue, much less. 

 As will be seen, I followed the ordinary method, but used more time. I am 

 satisfied that many of the so-called insuperable difficulties connected with 

 paraffine infiltration can be overcome by patience and time-serving. 



Turpentine, I did not find as satisfactory a reagent as chloroform, probably 

 because the latter will penetrate even if dehydration is not complete. I find 

 alcohol a stisfactory hardening reagent. McClatchie recommends the use of 

 chromic acid in hardening plant tissue. I failed to see its superiority over 

 alcohol. 



The staining was done mostly on the slide. Most of the ordinary nuclear 

 stains worked well. The most satisfactory stains all around were Czokor's 

 Alum Cochineal for the nucleus, and an alcoholic solution of bismarck brown 

 for the cell wall. When managed properly saflfraniu gave most beautiful 

 results. Alum-cochineal, borax-carmine, saffrauin, haematoxylin, fuchsin, 

 and picro-carmiue utterly failed to penetrate the specimens in mass. Orth's 

 lithium-picro-carmine was the only stain that penetrated in mass enough to 

 differentiate the structure of the embryo-sac. 



THE DEVELOPMENT OF THE AUDITORY VESICLE IN NECTURUS. 



BY H. W. NOKRIS. 



Owing to the lack of a complete series of embryos, T have been unable 

 to trace the earlier stages of the development of the ear. In all the 

 Amphibia, so far as studied, unless we except the species of Axolotl figured 

 by Houssay, and he was doubtless in error, the ear arises as a differentiation 

 of the inner of the two layers into which the ectoderm is early divided. 

 This inner sensory layer thickens on each side of the head so as to form a 

 small sensory tract, the anlage of the ear, closely analogous, if not homo- 

 logous, in formation to the lateral line sense organs. An ingrowth or 

 inpushing of the thickened ectoderm results in the formation of a pit. The 

 outer layer of indifferent ectoderm takes no share in the formation of the 

 auditory vesicle, but it is slightly involuted into the opening of the pit. 

 The pit deepens, its edges approach each other until the pit becomes a closed 

 vesicle. This description applies to development of the ear of the frog as 

 studied by Villy' and of the salamander, Amblystoma, as studied by myself=. 



1 Development of the Ear and Accessory Orsans of the Frog. Quart. .Four. MIc. 

 Sci..No. CXX.. 1890. 



2 Development of the Ear of Amblystoma. Jour. Morph., Vol. VII, No. 1. 1892. 



