CHEMICAL EFFECT ON GROWTH G DIFFERENTIATION 



163 



2. Strip eggs (Anura or Urodela) of their jelly membranes. Do not attempt to 

 remove the vitelline membranes, particularly of the Anura. The' stages 

 should be the same and in early gastrula {Anura #9 and Urodela #10). A total 

 of at least 300 undamaged eggs should be quickly prepared. (Since it takes 



5 hours to reach stage # 1 in the Anura, at least this much time should be 

 allowed for the denuding. ) 



3. Place 25 gastrulae in each of the finger bowls, and record the exact time 

 and stage. 



4. After 24 hours, pour off all experimental media and wash twice with control 

 medium. Finally place the embryos in 50 cc. of the control medium. 



5. Allow the embryos to develop under controlled conditions to Anura stage #22 

 or Urodela stage #40 (swimming), examine, and fix in 10% formaldehyde. 

 (Various degrees of exo-gastrulae, monorhyny and cyclopia will be found. ) 



6. The long exposure of 24 hours may prove to be too drastic for the species 

 used, as evidenced by the mortality and teratoligies of the experimental em- 

 bryos. For those solutions which produce such drastic effects, reduce the 

 exposure to 6 or even to 2 hours. 



DISCUSSION: 



Experiments in animalization and vegetalization have been standardized for the Echino- 

 dermata but Adelmann, Lehmann, and Hall have each demonstrated that Lithium Chloride 

 will effect the medium strip of organizer material of Amphibia resulting in exo-gastrulae, 

 which have faulty inductions (in consequence). A large variety of substances interfere 

 with gastrulation, but Lithium Chloride seems most satisfactory in the uniformity and 

 reproducibility of its effects. 



Hall (1942) has shown that even with Lithium Chloride the results will depend upon a 

 number of factors such as (a) concentration of Lithium (b) duration of exposure to the 

 salt (c) phase of development of the embryo (d) temperature of medium (e) presence of 

 other salts. The effect on differentiation is due to upsetting the delicately balanced de- 

 velopmental factors that are so important at the time of gastrulation, and the manifesta- 

 tions relate largely to the head and the tail organizers. By applying the Lithium Chloride 

 for 6 hour exposures at different stages of development, Lehmann has determined a shift 

 in susceptibility with progressive development. The effects are lessened at the lower 

 temperatures, and in the presence of calcium and the salts of the control medium. 



Figs. lo. embryo of 32 somites; lb. embryo of 8 mm. j 



Ic. embryo (in Mg) of about 12 mm. 

 Figs. 2a. embryo of 31 somites; 2b. embryo of 5. S mm. ; 



and 2c. embryo of about 9. 5 mm. 



All but Ic from lithium treatment. The "1" group exhibit 

 cyclopia complete and the "2" group exhibit cyclopia in- 

 complete. 



From Adelmann 1934: Jour. Exp. Zool 67:217 



CYCLOPIA IN AMBLYSTOMA 

 PUNCTATUM EMBRYOS 



