259] TURBELLARIA PROM THE MISSISSIPPI BASIN— HIGLEY 65 



seemed to have little effect on the development other than perhaps to hasten it. 

 This appeared true from the fact that in the hauls made every few days yoimg 

 individuals were constantly found in increasing numbers and of several sizes 

 up from those smallest and evidently just hatched. When isolated, the 

 individuals soon came to rest and easily accommodated themselves to the new 

 surroundings. Since the watch glasses were so small, there was some change 

 due to evaporation, but this was as slight as possible because they were con- 

 stantly watched and the water replenished or completely changed. In order 

 to prevent too much evaporation, they were kept covered with beakers. Part 

 of the time the water was changed every three or four hours, and part of the 

 time once in forty-eight hours. The water used to replenish was either clear, 

 from the reservoir which suppUed all the ponds, or else taken from the same 

 aquarium as the individuals themselves and then carefully freed from all 

 Crustacea and other small forms. 



At first the eggs were rolled around and moved by the force of the water 

 from the pipette. They then either floated for a Httle time or slowly sank 

 to the bottom. Two finally settled to the bottom and became fixed by a 

 secretion of cement, so that their position remained absolutely unchanged 

 thruout their incubation period. Others were rolled around more or less at 

 different times. The parents were removed from the watch glasses just as 

 soon as the egg was laid in order to prevent contamination of the water. Altho 

 the individuals were isolated at different times during the day, in all cases 

 the eggs were laid sometime late in the afternoon, the earhest at 2 :30, the others 

 about 5:00. It appeared that when the egg was ready or nearly ready for 

 laying, it required only a sHght disturbance of any sort to bring this about. 

 For example, in the case of egg number four, which was laid at 2:30 p.m., as 

 the stream of fresh water entered the watch glass from the pipette, the animal 

 somewhat aroused, contracted only slightly, but moved rather quickly about 

 the dish for a moment, and just that small amount of extra stimulation was 

 enough to cause the egg to be extruded. In all the other cases where the egg 

 was laid several hours later in the day, the parent was quiet, more or less 

 drawn up, clinging to the side of the glass or resting on the bottom. 



The eggs vary shghtly in shape, size, and color, showing perhaps the indivi- 

 dual character of the mother. Never quite spherical, they can hardly be said 

 to be ovoidal, the measurements averaging 145 by 140^. The outline 

 of the egg is thus a very round-ovoidal sphere. Sometimes, however, one 

 end is more pointed than the other, giving almost an ellipsoidal appearance. 

 That the shape is far from perfect was evident when the egg was rolled over 

 and there came into view variations in the outHne and in the amount of bulging 

 in the different parts of the siuiace. The color is a rather clear deep yellow, 

 verging a httle on the red and brown, and is lodged entirely in the shell. This 

 was demonstrated when the egg was broken and the white yolk was lost or 

 when the embryo escaped after hatching, leaving the empty yellow shell. To 



