56 WM. A. KEPNER AND W. H. TALIAFERRO. 



4. We can recognize two physiological conditions in Microstoma 

 caudatum Ldy.: ist, when it has its physiological tone; 2d, when 

 it does not have its physiological tone. In the first case it can 

 and does distinguish between its normal medium and an artificial 

 one such as .05 per cent, salt solution. In the second case it 

 does not make this distinction. 



5. This loss of physiological tone under laboratory conditions 

 is caused chiefly by the toxins thrown off by bacteria; if change 

 of temperature is a factor in this loss, it is but a slight one and in 

 time Microstoma adjusts itself to this change and regains its 

 physiological tone. 



6. The bilateral disposition of the ciliated pits serves to direct 

 the animal in its movements. 







LITERATURE. 

 Benham, W. B. 



'01 A Treatise on Zoology, E. Ray Lankester, Part iv. Platyhelmia, etc. 



London. 

 von Graff, L. 



'82 Monographic der Turbellarien. i. Rhabdocoelida. Leipzig. 



'09 Die Siisswasserfauna Deutschlands. Heft. 19. G. Fischer, Jena. 



'n Acoela, Rhabdocoela und Alloeocoela des Ostens der Vereinigten Staaten 



von Amerika. Zeitschrift f. wiss. Zoologie. Bd. 99. 

 Jennings, H. S. 



'06 Behavior of the Lower Organisms. Macmillan Co., New York. 

 Martin, C. H. 



'08 Nematocysts in Turbellaria. Quart. Journ. Mic. Sc., N. S., 206, Vol. 52, 



Part 2. 

 Ott, Harvey N. 



'92 A Study of Stenostoma Leucops O. Schm. Journ. Morph., Vol. 7. 

 Pearl, R. 



'03 The Movements and Reactions of Fresh- Water Planarians: a Study in 



Animal Behavior. Quart. Journ. Mic. Sc., Vol. 46. 

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'08 Beitrager zur Anatomic und Histologie der Susswassertricladen. Zeit. 



f. wiss. Zool., Bd. 89. 

 Weiss, Annie. 



'09 Beitrager zur Kentnis der Australisdren Turbellaria. Zeit. f. wiss. Zool., 



Bd. 94. 

 Wilhelmi, J. 



'08 Sinnesorgane d. Auriculargegend bei Susswassertricladen. Zool. Anz. 

 Bd. 33- 



