214 Vniversitij of California Publications in Zoology [Vol.11 



The natural assumption, and that suggested by Moquin- 

 Tandon (1846) in the above quotation, is that these undulatory 

 movements serve a respiratory function. Several dishes of Dina, 

 fed three days before, and hence in a normal condition, were 

 supplied with stagnant and to a certain extent putrid water 

 from a jar in the laboratory. Controls were used, supplied with 

 tap water. Within an hour all of the individuals in the foul 

 water either had been, or were, exercising undulatory movements, 

 while many of those in the dishes of tap water were quiet on 

 the bottom of the dishes, none of them having exercised undu- 

 latory movements. Foul water is not alone characterized by 

 low oxygen content, but by decomposition products as well. So 

 a similar series of experiments was conducted, using boiled water 

 instead of foul water. The same results were secured. After 

 the animals had been in the water for some time it wa-s observed 

 that their general tonus became lowered as the result of the 

 interference of the low oxygen content of the water with the 

 normal processes of the organism. As a consequence of this 

 condition, the animals showed more sluggish tendencies, remain- 

 ing quiet much more than was the case with the normal indi- 

 viduals in the control dishas. 



These experiments indicate that the movements have a 

 respiratory function, together, perhaps, with that of excretion, 

 enabling the nephridia more easily to discharge their excreted 

 substances to the exterior. An accessory function without doubt 

 is the removal of accumulating debris from the surface of the 

 body. In jars, where the material of this kind was loosened 

 from plants in removing specimens for experiments, it was ob- 

 served that the falling fragments were oftentimes the means of 

 inducing these movements which very effectively remove the 

 debris from the body. 



It is interesting to note that the undulatory movements were 

 observed to take place in a piece of only a few millimeters in 

 length, cut from the middle region of the body. 



6. Righting Reactions 

 The position in which the body of a nephelid comes in contact 

 with the surface of the dish determines very largely the nature 

 of the righting response. If the body is arched, as is often the 



