Xenopus laevis: An Excellent Laboratory Animal WAYNEWESTMARK Florida State University, Tallahassee

The search for suitable laboratory animals larger and progresses towards metamorphosis, has plagued high school biology teachers for the chromatophores become more numerous many years. The selection of an interesting as and eventually cover the entire animal. well as a useful demonstration animal presents The transparency of the animal is a feature even more of a problem. The indispensable that is invaluable in studying its anatomy and laboratory animal such as the leopard frog and morphology. All the organs of the head and the salamander are used in most all biology some of the organs of the trunk can be viewed and physiology classes. Even to the more so- by placing the animal in a half-filled petri dish Downloaded from http://online.ucpress.edu/abt/article-pdf/22/7/435/16747/4439384.pdf by guest on 30 September 2021 phisticated biologist the beauty of these ani- and putting it under a binocular dissecting mals is never lost. However, the student may microscope. This gives the student the oppor- become bored with seeing these routine lab- tunity to study the organs at any time as well oratory animals every day. One way of solving as to make an over-all study of metamorphosis. such a problem is to bring to the lab in- Of particular interest are the heart, eye teresting specimens, a very good example of (optic nerves), otic capsule, chromatophores, which is the tadpole of the Xenopus laevis, or and the circulatory system. All of these struc- the South African clawed toad. tures are clearly visible under a dissecting The tadpoles are entirely transparent ex- microscope. cept for a few random chromatophores on the This animal is quite adaptable to laboratory dorsal part of the body. As the animal grows conditions and requires only a small amount of care. The adult frog is strictly carnivorous, feeds only while in the water and is entirely aquatic. The frog gets its name from the fact that it has clawed toes; it has neither teeth nor tongue. The frogs may be kept in a small, square or round aquarium with several inches of water. They may be fed a varietv of things such as ground beef, beef liver, beef kidney, and pork kidney, and should be fed once or twice a week. The water should be changed in the aquarium 12-24 hours after each feeding to prevent fouling of the water. In its natural habitat the male frog stimu- lates the female frog in the early spring. However, these animals can be bred success- fully in captivity with high yields of eggs throughout the year. The female is injected with 400-600 units of chorionic gonadotrophin and the male with 200-300 units. For best re- sults the needle should be inserted just under the skin on the posterior dorsal part of the hind leg and passed cephalad just anterior to the cloacal opening. Inject the gonadotrophin into the lymph sac and place the animals back in the water to spawn. In 6-8 hours the egg laying should be at its maximum. After the spawning is completed, remove the eggs to Figure 1. Dorsal view of mature tadpole. fresh clean water. Within five days the yQung 435 436 THE AMERICAN BIOLOGY TEACHER October, 1960

As the tadpoles feed, they assume a diagonal position in the water. This "head down" posi- tion is due to the extra large head of the tad- pole making them "front heavy." To counter- balance this unequal distribution of weight, the tadpole maintains a constant, rapid whip- like motion of the extreme tip of the tail. This prevents the animal from sinking head first to the bottom of the aquarium. This whip-like motion of the tip of the tail is not to be con- fused with the undulating movements of the

entire tail which propel him through the Downloaded from http://online.ucpress.edu/abt/article-pdf/22/7/435/16747/4439384.pdf by guest on 30 September 2021 water. Figure 2. Dorsal view of various stages of meta- Liver powder is the best food to use for morphosis of the tadpoles. these animals since it can be purchased ready tadpoles should be free swimming larvae. to use. Unless the tadpoles are overcrowded, At this stage they are ready to begin feed- 1 mg. of liver powder per animal per day is ing. It is interesting to observe that within an sufficient for normal growth. If the aquarium hour after food has been added to the aquari- becomes fouled due to excess food, the amount um, the animals begin to surface and take will have to be lessened. The water should gulps of air. This marks the point at which never need changing if the proper food intake they start using their lungs. is maintained.

Salt Water tive and positive ions (charged fractions of the A new laboratory machine that can split mineral molecules) on either side. With greater the salt and essential minerals from sea water separation, pure water is collected at the cen- -and that may make possible a multiple vac- ter; sodium calcium and magnesium hydroxides cine against communicable diseases-has been are collected on one side, and chlorine and described. The "spectrolator," as the machine bromine gases and certain acids on the other. is called, separates mixtures of substances bv Thus the spectrolator makes possible, simul- means of combined chemical and electrical taneously with salt water conversion, the ex- methods, Dr. Arthur Karler, chemist and bio- traction of the many essential minerals present physicist, of the Karler Laboratories, Berkeley, in unlimited supply in ocean water. Calif., said. "It actually splits up various substances into component fractions somewhat as a glass prism Science Encyclopedia separates white light into its characteristic The McGraw-Hill Book Company an- spectrum of rainbov colors," Dr. Karler ex- nounced that it has finished and sent to the plained. The main part of the apparatus is a printer the manuscript of the largest technical filter paper curtain, he said. A solution is fed publication ever undertaken in the English in at the top, and a continuous direct elec- language-an Enicyclopedia of Science and trical current passes across the fluid as it runs Technology. down the curtain. The degree of separation The work will be published in fifteen large of the fluid components is governed by the volumes this fall and will contain 7,224 articles electrical voltage and the speed at which the written by some 2,000 authorities on their re- fluid is fed. spective subjects. The work of these contrib- "Each component builds up its own path utors was guided by a large corps of consulting through the curtain, to be collected in a pur- editors, each a specialist in one of 62 assigned ified state at its respective position across the fields of mathematics, engineering, physical curtain," Dr. Kaler said. "As as example, if science, life science, earth science, agriculture, ocean water is processed, the yield would be conservation, meteorology, space technology, pure water at a center drip point, with nega- etc.