NOTES ON METHODS FOR THE STUDY OF AMPIIIBTAN 

 EGGS AND LARVAE.^ 



BY ALBERT KUNTZ. 



In the prepration of amphibian eggs and larvae for histological study, 

 the technique employed is a factor of primary importance. The am- 

 phibian egg represents the final attempt on the part of nature to pro- 

 duce a large yolk-laden egg in which cleavage involves the entire ovum. 

 As a result of this method of cleavage all the embroynic tissues, during 

 the early stages of development, contain more or less yolk. Further- 

 more, the ventral region of the young embryo contains a large, com- 

 pact yolk-mass which is not readily penetrated by the fixing and the 

 clearing agent, and the embryonic tissues show a greater tendency to 

 shrink than do the tissues of other vertebrate embryos. 



In the preparation of this material it is essential to select a fixing 

 agent which will penetrate the yolk readily, but which will not cause 

 the tissues to shrink. In the process of dehydration, high per cent 

 alcohols must not be employed longer than is absolutely necessary. A 

 clearing agent must be selected which will clear the yolk, but which 

 will not render the tissues unduly brittle. In the process of imbed- 

 ding, thorough impregnation must be secured without subjecting the 

 tissues for too long a time to high temperature. 



In the course of an investigation of the development of the sympa- 

 thetic nervous system in the Ambhibia,^ the writer has had the oppor- 

 tunity to compare the results obtained from various methods of tech- 

 nique. Ambhibian eggs and embryos fixed and deh|ydrated in the 

 usual manner show a great tendency to shrink. As a clearing agent, 

 xylol is unsatisfactory because it does not clear the yolk readily and 

 renders the tissues unduly brittle. The method which was found to 

 yield the most satisfactory prei)arations of amphibian embryos for 

 general microscopic study is a modification of the method described 



^From the Laboratories of Animal Biology of the State University of Iowa. 

 ''The development of the sympathetic nervous system in the Amphibia. Jour. 

 Comp. Neur., vol 21, no. 4. pp. 397-416. 

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