15. Compare a fresh-hatched tadpole with one in which the hind limbs have recently appeared. (1898) 16. Trace the history of a tadpole from hatching to the time when the tail begins to grow less. What does it feed upon during this time? (1898) 17. Relate the life-history of the frog, from the time of hatching to the end of the first summer. (1897) 18. Give some account of the habits of a young tadpole a few days after hatching, especially with respect to locomotion and feeding. Make a drawing of such a tadpole in side view, three times the natural length. (1904) 19. Describe the hind leg of a frog, and explain the ways in which it is used. (1905) 20. Show how a full-grown frog is enabled to live either in air or in water. (1906) [Pg 349] CHAPTER XIX. THE HABITS AND LIFE-HISTORIES OF COMMON INSECTS. 62. THE COCKROACH: A TYPICAL INSECT. 1. Habits.—In what places have you seen cockroaches? Are they often to be seen during the day, or do they, in general, come forth only at night? What is the colour of the body? Put a live cockroach under a tumbler, and watch its movements. In what position is the head held? Notice the long feelers; how are they used? Look at the lower part of the head, and try to see the palps, which resemble small feelers. How many legs has the cockroach? Watch the rhythmical movement of the hinder part of the body. Soak a small piece of bread in milk or water, and put it under the tumbler; watch the cockroach feed. How does it use the palps? Notice that the jaws move from side to side. How does the insect clean itself? 2. External characters.—Put a cockroach into a test-tube, and dip the tube into boiling water; this kills the insect instantly. Notice the thin “shell” which covers the outside of the animal. Make out that the body consists of (a) head, carrying the eyes, feelers, and jaws; (b) thorax, carrying the wings and legs; and (c) abdomen. Examine them in turn. (a) The head.—Notice the vertical position, the black, kidney-shaped eyes, the feelers, the “upper” lip (labrum), and the small, blackish mandibles at the sides of the labrum. Pass your knife-point close behind the labrum and into the mouth, and see the “lower” lip (labium), which lies behind the knife, i.e. behind the [Pg 350] mouth. Cut off the head and carefully strip off the labium. Put it on a sheet of paper and examine it with a lens, comparing it with Fig. 222 (Mx. 2). Examine the same head from behind with a lens and see the pair of first maxillae. Notice how they are attached to the head, and then remove one and compare it with Fig. 222 (Mx. 1). Work one of the mandibles backwards and forwards with the point of a pin, and then remove it and examine it with a lens to see the toothed inner margin.