Apeil 3, 1903.] 



SCIENCE. 



531 



descent lamps varying in intensity from 

 192 candle-meters to .012 candle-meter; 

 the percentages of negative head move- 

 ments referable to light of different in- 

 tensities are as follows: 41.5 per cent. (192 

 cm.), 41.5 per cent. (90 cm.), 59 per cent. 

 (48 cm.), 45 per cent. (31 cm.), 45.5 per 

 cent. (12 cm.), 38.5 per cent. (5 cm.), 24.5 

 per cent. (1 cm.), 14 per cent. (.128 cm.), 

 12 per cent. (.050 cm.), 5 per cent. (.020 

 cm.), and 3 per cent. (.012 cm.). A. 

 fogtida is positively phototropic toward an 

 electric incandescent light of .001 candle- 

 meter intensity. Earthworms retreat into 

 their burrows during daytime because of 

 their negative phototropism. They emerge 

 at night not so much because of darkness, 

 but because of their positive phototropism 

 for faint light. 



The Collembola Fauna of Cold Spring 

 Harbor Beach: C. B. Davenport, Uni- 

 versity of Chicago. 



The apparently lifeless surface of the 

 between-tide zone of this sandy beach sup- 

 ports a vast host of minute insects belong- 

 ing to the family Poduridse. These ani- 

 mals crawl out to the surface after the 

 retreat of the tide and return again into 

 the sand as the tide rises. The period 

 which they spend on the surface is spent 

 in ceaseless activity, and the direction of 

 all this complex movement is determined 

 by the resultant of the physical agents by 

 which they are surrounded. They are 

 geotactic, hydrotactic, rheotactic, thigmo- 

 tactic and phototactic in the highest de- 

 gree. This extreme sensitiveness of organ- 

 isms closely related to the ancestors of in- 

 sects is suggestive in view of the complex 

 nervous mechanism and reactions attained 

 by their most highly developed descendants. 



The Function of the Pearl Organs of the 

 Cyprinidce: Jacob Reighakd, University 

 of Michigan. 

 Pearl organs are found in the breeding 



males of many fish, but only rarely in the 

 females. The breeding behavior of three 

 forms was studied, Campostoma anomalum, 

 Rhinichthys atronasus and Semotilus atro- 

 mac'ulatus. 



The organs in all these eases are spines 

 and in each case they were found to have 

 a mechanical function. They are used in 

 Campostoma in building the nest, in the 

 battles of the males and in holding the fe- 

 males during the act of spawning. In 

 Semotilus and Rhinichthys they are used 

 in holding the spawning female. The 

 method of holding the females is different 

 in each of these three cases, but in each 

 case the distribution of the pearl organs 

 corresponds to this mechanical use. 



Phototaxis in Volvo f: S. J. Holmes, Uni- 

 versity of Michigan. 



In light of weak or moderate intensity 

 Volvox is positively phototactic and orients 

 itself very accurately to the direction of 

 the rays. In swimming towards the light 

 the anterior end of the organism is di- 

 rected forwards, the body rotates on its 

 longer axis, and deviates remarkably little 

 from a perfectly straight course. In 

 very strong light Yolvox, becomes nega- 

 tively phototactic, swimming away from 

 the light in very nearly a straight line. 

 The grouping of Volvox in places of a 

 certain intensity of illumination is a 

 natural consequence of the fact that this 

 organism is positively phototactic in weak 

 light and negatively so in strong light. 

 In very dim light Volvox shows no pro- 

 nounced phototaxis, and either lies quiet or 

 rolls about in a slow and irregular manner. 

 In moving towards the source of light the 

 rate of locomotion, within certain limits, 

 increases with increase in the intensity of 

 illumination, but, as the optimum is ap- 

 proached, the speed becomes gradually less. 

 In swimming away from strong light the 

 speed is likewise lessened as the optimum 



