Disappearance of the tail.—From the first to the middle of June the tadpoles should be watched with especial care, for wonderful things are happening. Both the fore and hind legs will appear, if they have not already. The head will change in form and so will the body; the color will become much lighter, and, but for the tail, the tadpole will begin to look something like its mother.
If you keep an especially sharp lookout, do you think you will see the tail drop off? No, toad nature is too economical for that. The tail will not drop off, but it will be seen to get shorter and shorter every day; it is not dropping off, but is being carried into the tadpole. The tail is perfect at every stage; it simply disappears. How does this happen? This is another thing that it took scientific men a long time to find out.
It is now known that there are two great methods for removing parts of the body no longer needed. In the first method the living particles in the body which are able to wander all around, as if they were inspectors to see that everything is in order, may go to the part to be removed and take it up piece by piece. These living particles are known as white blood corpuscles, wandering cells, phagocytes, leucocytes and several other names. In the other method, the blood and the lymph going to the part to be removed dissolve it particle by particle. Apparently the toad tadpole's tail is dissolved by the blood and lymph rather than being eaten up by the phagocytes, although the phagocytes do a part of the work.
Fig. 114. Transforming tadpole of the green tree toad to show the rapidity of tail absorption. (Change in 24 hours. Natural size.)
HVLA—Natural size. Change in 24 hours; 28 mm. of tail absorbed in 24 hours; 11/6 mm. per hour. Common toad shortens the tail about 1/5 mm. per hour.
Now, when the tadpole is ready to dispense with its tail, the blood and lymph and the phagocytes take it up particle by particle and carry it back into the body where it can be used just as any other good food would be. This taking in of the tail is done so carefully that the skin epithelium or epidermis is never broken, but covers up the outside perfectly all the time. Is not this a better way to get rid of a tail than to cut it off?
If you look at the picture of the disappearance of the tail in the toad tadpole ([Fig. 115]) and in the tree-toad tadpole ([Fig. 114]), you will get an idea how rapidly this takes place. It is easier to see the actual shortening if the tadpoles are put in a white dish of clear water without any water plants. The tadpoles do not eat anything while they are changing to toads, so they will not need to be fed.
Beginning of the life on the land.—Now, when the legs are grown out, and the tail is getting shorter, the little tadpole likes to put its nose out of the water into the air; and sometimes it crawls half way out. When the tail gets quite short, often a mere stub, it will crawl out entirely and stay for some time in the air. It now looks really like a toad except that it is nearly smooth instead of being warty, and is only about as large as the end of a child's little finger ([Fig. 115]).
Finally, the time comes when the tadpole, now transformed into a toad, must leave the water for the land.