118 INTRODUCTION TO GENETICS OF MAN AND FRUIT FLY 



Exercise XXII 



of absorbent cotton or paper taped on the in- 

 side. A drop or two of ether is put on the 

 cotton or paper, and the dish is placed over the 

 flies for a few seconds. Alternatively, the flies 

 can be covered with the open chamber of the 

 plastic etherizer. Flies are more easily killed by 

 a second exposure to ether than by the first, so 

 be particularly careful not to overdo it. 



The anesthetized flies should be dumped out 

 of the etherizer onto a white paper card and 

 examined under the dissecting microscope; use 

 whatever magnifications are convenient. The 

 flies are moved around on the card with a 

 camel's hair brush or a dissecting needle. When 

 dividing the sexes, it is convenient to line up 

 all the flies at the center of the card and then 

 to run down the line pushing males to one side 

 and females to the other. 



REGENERATION OF PLANARIA 



Planarians have a remarkable capacity to re- 

 generate parts of their bodies which have been 

 removed. Regeneration occurs in all animals, 

 yet to diff"erent degrees, tending to diminish as 

 one ascends the evolutionary scale, until in 

 mammals it is restricted to wound-healing. 



Planarians are members of the phylum 

 Platyhelminthes, the flatworms. (For their sys- 

 tematic position, see Weisz, pp. 731-732; 

 S. P. T., pp. 528-531 ; Villee, pp. 201-203.) They 

 are small animals, less than an inch long, and 

 have a primitive brain, eyes, digestive organs, 

 muscles, and an excretory system. They repro- 

 duce either sexually or by fragmentation. 



Our planarian is Dugesia dorotocephala, a 

 relatively large species that is uniformly darkly 

 pigmented. It is found in the middle-western 

 states in wells or spring-fed streams. In the 

 laboratory, planarians are kept in spring water 

 or dechlorinated water, and are fed occasionally 

 on bits of beef liver. During the course of 

 regeneration, however, they should be starved. 



Each student will be given two or three 

 animals. It will be up to you to design your 

 own experiments to demonstrate regeneration. 



This laboratory guide is only to suggest possi- 

 bilities. Everyone should read the chapters in 

 Buchsbaum's book before coming to the labora- 

 tory in order to see the variety of simple experi- 

 ments that can be done. After the initial opera- 

 tions have been performed, the animals must be 

 disturbed as little as possible. If you would 

 rather carry out this experiment at home, per- 

 form the surgery there also. 



Before operating on the animals, you might 

 determine their sensitivity to light. They have 

 well-defined eyes, which can discriminate bright- 

 nesses and the direction from which light comes, 

 but which probably do not resolve images. Use 

 the lamp from the dissecting microscope as a 

 light source. Simpson, Pittendrigh, and Tiffany 

 (p. 240) and Buchsbaum (pp. 118-120) describe 

 several experiments on the behavior of these 

 animals, even one experiment that suggests 

 learning. You might want to repeat these or to 

 devise experiments of your own. 



Planarians are best observed under low powers 

 of the dissecting microscope, in either a small 

 petri dish or on a slide. Be sure to use a prepara- 

 tion of bicarbonate-versene-tap water (BVT) and 

 never the untreated tap water, which may kill 

 them. They are best transferred from one con- 

 tainer to another with a small camel's hair 

 brush, or with a bit of tissue paper grasped in 

 forceps so as to serve as a brush. To make a 

 cut, wait until the animal has flattened out, and 

 then make a quick slash, perpendicular to the 

 plane of its body, with a clean, sharp razor 

 blade. After the operation, transfer the animal 

 or its parts to the containers and label them 

 carefully. Keep them cool, though not cold, 

 and in little or no light. The water should be 

 replaced two or three times a week with fresh 

 BVT, and dead animals must be removed at 

 once. Do not feed them during the month or so 

 it will take to complete regeneration. The ani- 

 mals should be left in the laboratory and dis- 

 turbed as little as possible. They are quite 

 fragile after the operation and will disintegrate 

 if shaken. 



Experiments of this kind have disclosed a 

 number of principles which govern regenera- 



