Zool— Vol. I.] RITTER—DIEMYCTYLUS TOROSUS. 85 



when the conditions are such that one's foot-falls produce a 

 slight jar, either to the water itself or to the bottom on which 

 the creatures may be resting, they will swim or run away 

 for a short distance as one approaches them. 



From various tests and observations I do not believe that 

 the sense of sight is of much use to them in distinguishing 

 objects, excepting for short distances — not much beyond a 

 foot it appears — for objects the size of a man's hat. 



They are in no sense given to hiding themselves from 

 the light of day. During their aquatic career it seems to 

 be their chief care to dwell in still waters. Nowhere have 

 I seen them in any such abundance as in the reservoir al- 

 ready mentioned; and this lies out perfectly free to the full 

 light of day, and there is almost nothing in or about the 

 water that can be used as a hiding place or a screen from 

 the daylight. It seems hardly possible that they are in- 

 duced hither by a particular abundance of food, since 

 great care is taken by the water company to keep the re- 

 servoir as free from life of all kinds as possible. I may 

 mention that the "water dogs " are taken out in great num- 

 bers, as I am told by the Italian workman who lives at the res- 

 ervoir as an employee of the company, and buried in the 

 ground to prevent their getting back to the water, the fear 

 being, of course, that they are in some way injurious to the 

 water. As a matter of fact, however, their presence is 

 rather an advantage, since they undoubtedly act as scaven- 

 gers for the water, so far as animal life is concerned. 



When living on land they often make long excursions 

 out into open areas ; e.g., they are familiar objects to every- 

 body about the University of California, so frequently are 

 they seen slowly and silently strolling about the grounds 

 and over the sidewalks. At such times they do not mani- 

 fest the least inclination to escape being captured; indeed, 

 I have sometimes imagined them to be presenting them- 

 selves as museum or laboratory offerings. 



2. Seasonal Changes. — As a considerable part of the 

 interest attached to the results of my studies on the seasonal 

 characteristics of our Dicmyctylus consists in the compar- 



