54 University of California Publications in Zoology [VOL. 13 



used the "heizbaren Objekttisch" of M. Schultze and sometimes did 

 not, and that he was never able to keep the animals alive for more 

 than two or three hours at the most. 



Giinther (1899 and 1900) says even less about his methods than 

 does Bundle (1895). Both investigators found that the alcoholic 

 corrosive-sublimate solution gave the best results as a fixing agent 

 and were inclined to the use of haematoxylin as the most satisfactory 

 stain. 



In my study of the living animals use has been made of an auto- 

 matic constant-temperature warm oven slightly modified from the 

 pattern used by Dr. J. A. Long (1912) in his study of the living eggs 

 of rats and mice. The adjustment of the automatic temperature regu- 

 lator is such that the temperature of the material on the slide may be 

 kept constant to within 0.5 C. for an indefinite period of time. The 

 great advantages that such an apparatus offer are: first, that not 

 only the material under actual observation, but also the remaining 

 material, the microscope stage, the slides, the cover glasses, the pipettes, 

 etc. may all be kept at the desired constant temperature, and second, 

 that the temperature under w r hich the animals are being studied, can 

 be easily raised or lowered as desired, at the will of the observer. 



When the fluid to be studied is brought from the slaughter house 

 to the laboratory, it is immediately put into this warm oven so that 

 from the time of leaving the stomach to the time of being placed on 

 the slide, the loss in temperature is not greater than 0.5 C. and once 

 on the slide, the drop of fluid may be studied for from eight to ten 

 hours without any apparent injury to the animals. A second impor- 

 tant use, as noted above, to which this apparatus may be put and a 

 most necessary one in studying the movements of the living animals 

 is that of temperature control. Under normal conditions the exceeding 

 great liveliness of these organisms makes their accurate study ex- 

 tremely difficult. Various investigators have recommended the ad- 

 dition of some substance such as a watery solution of cherry tree gum, 

 a three or four percent solution of gelatin, Irish moss, quince seeds, 

 etc., which would eliminate or at least diminish the constant motion of 

 these animals. All of these methods have been tried by me with more 

 or less success, but with the inevitable result that the longevity of the 

 organisms has been decreased. By means of the above described con- 

 stant-temperature oven, however, the operator can regulate the temper- 

 ature to such a degree that the activity of the animals may be almost 

 absolutely controlled without any apparent injurious effects. To 



