CHAPTER XII 

 DEVELOPMENT OF THE TOAD 



FIELD AND LABORATORY EXERCISE 



TECHNICAL NOTE. As the work of this chapter, or some similar 

 work in getting acquainted with the postembryonic development 

 of a many-celled animal, should be done early in the course, and 

 as most schools open in the fall, it will perhaps be impossible to 

 make this first study of development from live specimens in the field. 

 In such case the examination of a series of prepared specimens, 

 previously obtained by the teacher, must be resorted to. In the 

 spring the development of several kinds of animals, including the 

 toad, can be studied from live specimens in the field or in breeding- 

 cages and aquaria in the laboratory. The eggs of the toad may be 

 found in April and May (the toads are heard trilling at egg-laying 

 time) in ponds. The eggs look like the heads of black pins, and are 

 in single rows in long strings of transparent jelly, which are usually 

 wound around sticks or plant-stems at the bottom of the pond near 

 the shore. Bring some of these strings into the schoolroom and 

 keep them in water in shallow dishes. Keep them in the light, but 

 not in direct sunlight. In the dishes put some small stones and 

 mud from the pond, arranging them in a slope, thus making different 

 depths of water. Stones with green algae on should be selected, for 

 algae are the food of the tadpoles. The eggs will hatch in two or 

 three days, and if too many tadpoles are not kept in the dish, and 

 the little aquarium be well cared for, the whole postembryonic de- 

 velopment of the toad can be well observed. For the study of the 

 development from prepared specimens the teacher should have a 

 complete series of stages from egg to adult toad in alcohol. The 

 specimens may be examined by the students in connection with a 

 talk from the teacher on the life-history of the toad. 



If the study is made from prepared specimens, make 

 drawings of egg-strings, and of a single egg magnified 

 and shaded to indicate its color. Draw each specimen of 

 the series of tadpoles, noting in the youngest the presence 

 of gills and tail and absence of legs and eyes; in the 



55 



