247] TURBELLARIA FROM THE MISSISSIPPI BASIN— HIGLEY S3 



Specimens were taken from the ponds in pails of water in the common 

 way and then, one by one, removed with a pipette to small watch glasses or to 

 a slide. For study alive, they withstand the presence of the cover glass better 

 than other forms, since they do not easily or quickly break. Quince-seed jelly 

 is not practical as only an extremely thick solution has any efifect on the strong 

 muscular movements. The best method is perhaps to quiet them with solu- 

 tions of cocaine and chloretone. They are very resistant to anything of this 

 sort and it requires large doses to produce a condition of quiet, and then disin- 

 tegration is likely to begin in a comparatively short time. When the animals 

 are to be killed, corrosive acetic or cold corrosive solution used directly after 

 they have become quiet under the anesthetic will cause httle contraction. 

 They can then be stained, cleared and mounted in to to, and most of the organs 

 will be fairly distinct. Sections were cut from four to eight micra in thickness 

 and were stained in Ehrlich's hematoxylin and erythrosin. 



The length was taken when the animal was at the point of greatest exten- 

 sion or at least when moving unhampered freely thru the water, so that both 

 anterior and posterior tips were drawn out to acute points. A number of 

 very small individuals were considered juveniles and not merely shrunken in 

 size, due to lack of food. This seemed to be the case, since under starvation 

 conditions there is very little shrinkage of body size, most of the change being 

 in relative amount of bulging in the intestinal wall. Those specimens ap- 

 parently adult will vary from 1 to 2 mm. in length, the average being within 

 rather narrow hmits, 1.3 to 1.6mm. The width is perhaps a Httle more difficult 

 to compute, since it varies with physiological conditions, i.e., it depends upon 

 the amount of food recently taken in and also stage of development of the 

 reproductive organs. The limits of variation here are from 0.1 to 0.35 mm, 

 the average being 0.2 to 0.35 mm. The greatest depth is very nearly the same as 

 the greatest width, for altho the ventral surface is flat and the anterior part 

 low, the portion of the body posterior to the middle is much elevated so that 

 it is nearly cylindrical. Both the measurements of width and depth were 

 taken at a point slightly posterior to the pharynx. 



The amounts of expansion and contraction are very great so that measure- 

 ments mean little except in a general way. A significant detail with respect 

 to shape is the amount of food in the intestine, or at least the abundance of 

 food at previous times. This correlation of nourishment supply with shape 

 variation is the result of the flexibility of the assimilative cells. Under starva- 

 tion conditions they are very minute and occupy no appreciable space in the 

 body structure. When, however, the digestive sac is distended with nutrient 

 material, these cells enlarge from five to ten times, and give the characteristic 

 plump appearance to the animal as a whole. This species is especially con- 

 tractile, so that it is able very quickly to accommodate itself to its surroundings. 

 Under the shghtest disturbance or fright it may be drawn into an almost per- 

 fect sphere, the tips of the head and tail being only the merest knob-Uke pro- 

 jections on the surface. The hmits of extension are very much narrower 



