10 ILUNOIS BIOLOGICAL MONOGRAPHS [204 



intervals. Varied amounts of sunlight were used. A few jars were placed so 

 as to have sun all day but most had it for only a few hours at a time and a 

 good many not at all. Generally the temperature of the aquaria was that of 

 the room; a few however were held at a much higher and a few at a much lower 

 point. Balanced and favorable conditions are always easy to obtain, and in 

 a number of cases there was a good deal of asexual reproduction by budding, as 

 a result of fairly perfect metabolism. Occasionally when a number of sur- 

 rounding details were precisely favorable, even the sexual reproduction could 

 be studied and the life habits made out with some degree of completeness. 



The aquaria were never artificially aerated, but an attempt was always 

 made to furnish oxygen by means of plant life. In the case of Planaria food 

 was provided in the shape of small bits of meat, while in the jars where rhab- 

 docoels were living there was always an abundance of other animal forms to 

 supply aU possible needs. 



In preparation for histological study the specimens were killed and fixed 

 with some measure of success. The individuals in some cases were anaesthe- 

 tized with a solution of cocaine hydrochlorate followed by chloretone of varying 

 strengths until they were quiet and expanded. The fixation was done with 

 corrosive acetic solution. Material was generally stained in toto with Ehr- 

 lich's hematoxyUn, embedded in paraffin, and sectioned 4 to Sn in thickness. 

 A counterstain of eosin or erythrosin was sometimes used. With Planaria a 

 solution of one part nitric to three of water gave good results as a killing fluid. 

 Cold corrosive sublimate was found useful in many instances, and under special 

 conditions a warm solution was valuable. 



METHODS OF STUDY 



Specimens were studied either alive or in permanent mounts. When living 

 they were controlled by means of a pipette and were isolated either in concave 

 watch glasses or on a sUde. The movements could be checked by burying in 

 a drop of quince-seed jelly or by adding small amounts of cocaine or chloretone 

 to the water. The jelly is of value in studying the ciHa or the muscular system, 

 for it increases the violence of action while retarding the speed. It also shows 

 more clearly the relative position of various organs, for the animal will turn 

 over again and again, thus affording good lateral and ventral views. The 

 objection to its use lies in the fact that only a very thick, opaque solution will 

 be dense enough to reduce the movement appreciably. The chloretone has 

 the advantage of quieting the worm thoroly, but it also causes the specimen 

 to become so Hmp as to be easily injured, and to begin to disintegrate very soon. 

 Another way is to confine the animal by the weight of the cover glass or by 

 using a minimum amount of water on the slide. This method flattens the 

 body so as to make it more transparent, and also pushes the several organs 

 entirely out of their natural position. But organs can be studied in this way bet- 

 ter than under any other conditions, since they can be partially isolated and 

 their interrelationships made out. Because of the transparency and lack of 



