496 APPENDIX 



tions. Try also the effect of touching the nerve with a hot 

 wire and with a drop of dilute acid or alkali. During experi- 

 mentation the nerve preparation must be kept moistened with 

 the salt solution. 



CHAPTER XXIII 



The structure of the egg may be studied in the starfish or 

 sea urchin, frog or fowl. Starfish eggs preserved in various 

 stages of segmentation may be purchased from the Department 

 of Laboratory Supply of the Marine Biological Laboratory at 

 Wood's Hole, Mass. Frogs' eggs may be found in ponds and 

 ditches in early spring. If transferred to the laboratory and 

 kept supplied with fresh water they may be watched through 

 their various stages of segmentation to the formation of the 

 tadpole, its liberation from the egg, and its later development. 

 Compare with Fig. 370. To watch the development of a chick, 

 eggs may be incubated by a hen or in an artificial incubator, one 

 egg being removed each day, and opened by breaking away a cir- 

 cular piece of the shell on the upper side. If kept submerged in 

 a dish of .75 per cent salt solution, warmed to the temperature 

 of the body, the embryo chick may be kept alive for several 

 hours to show the beating of the heart, etc. (Figs. 365, 366). 



