EYE FIELD OPERATIONS 293 



bi-weekly intervals, and notations made on general coloration. Measurements 

 can be made rapidly by pasting millimeter graph paper on the underside of a 

 flat-bottomed finger bowl (or Petri dish) into which the larva is placed for a quick 

 total length measurement. 



If facilities and time allow, there are other variables to this experiment: 



1. Instead of using a black-painted cover for the darkened finger bowls, cover them 

 with glass (of Wratten celluloid) color filters which allows various monochroma- 

 tic radiations through to the larvae to determine the relative value of parts of the 

 spectrum in pigmentary response. 



2. The eyes may be removed and transplanted to heterotopic positions, where they 

 do not acquire nerve connections with the central nervous system, to determine 

 whether they then function in pigmentary response. 



3. The dark and light-adjusted enucleated (and normal) larvae may be transferred 



to the opposite environment (dark to light and vice versa) to determine the degree 

 of adaptability (adjustment) in respect to a definite time interval. (Detwiler & 

 Copenhaver in 194Z state that dark-adapted eyeless larvae are pale but darken in 

 moderate lighting, while dark-adapted normal larvae tend to become lighter 

 colored in moderate lighting. ) 



The conclusions from this set of observations should relate both the growth rate and to 

 the pigmentary responses of eyeless larvae. 



THE EXPERIMENTAL PRODUCTION OF CYCLOPIA 



Adelmann (1936) states: "The hope of one day attaining an adequate understanding of cy- 

 clopia is considerably strengthened by two important considerations, first, the fact that 

 the anomaly may be experimentally produced with considerable ease, and secondly, the 

 fact that experinientally produced cyclopean monsters exhibit essentially the same fea- 

 tures as those spontaneously arising. " Stockard (1907 to 1910) produced cyclopean fish 

 with various concentrations of NaCl, LiCl, NaOH, and ainyl alcohol. Others have used 

 acetone, and butyric alcohol and even physical variables. Amphibian cyclopean monsters 

 have been produced by treating the eggs with lithium chloride, ethyl alcohol, chloralhy- 

 drate (LePlat, 1919, Cotronei, 1922, Guareschi, 1934, and Adelmann, 1934) phenol and 

 chloretone (Lehmann, 1933). 



Cyclopia can also be produced by surgical interference with early cleavage stages up to 

 gastrulation, by constriction (Spemann, 1904), and by excision of parts of the archenteric 

 roof (Mangold, 1931). 



The experimental procedure is in general to expose the early blastula of any Amphibian 

 to from 0. 2% to 1. 0% LiCl for periods up to 24 hours, then returning them to normal 

 medium whereupon many of the surviving embryos will develop cyclopia. The effect is 

 essentially one of vegetalization. Since the procedure is described in detail under "The 

 Chemical Separation of Growth and Development" it will not be further discussed here. 



DISCUSSION: 



The embryonic eye is inade up of two major parts, each of which originates from the ecto- 

 derm. The optical vesicle is the first to develop, being an evagination from the dien- 

 cephalon. When this brain ectoderm makes contact with the overlying head ectoderm it 

 "induces" the thickening of this ectoderm to form the lens placode. (See exception under 

 the term "double assurance"' in the Glossary. ) This placode then invaginates to form a 

 lens vesicle which becomes incorporated into the developing optic cup. The head ectoderm 



