394 S. J. HOLMES 



reactions of particular organs to light, destroys the phototaxis 

 of the organism. 



Issel (19) has studied the habits of a small isopod, Zeno- 

 biana, which lives in holes in marine plants which it is thought 

 to excavate. The isopods are more active during the night. 

 Shadows cause them to retreat quickly into their tubes. They 

 are stiongly thigmotactic and exhibit the instinct of feigning 

 death. Theie are a number of interesting structural adapta- 

 tions and instincts in relation to a tube-dwelling life. 



Jackson (20) writes a general account of the natuial histoiy 

 of Hyalella knickerbockeri (Bate), treating of general distribu- 

 tion and local habitat, color changes, size in 1 elation to sex, 

 methods and frequency of molting, breeding habits, food and 

 feeding, enemies, thigmotaxis and locomotion. 



Jacobs (21) finds the resistance of different species of Protozoa 

 to C0 2 vaiiable. The contractile elements in Vorticella and 

 Peranema are soon paralyzed, but the cilia and flagella are 

 moie resistant. In Vorticella, however, the contractile elements 

 are first stimulated and then paralyzed; the vibratile ones are 

 temporarily stopped and then started again. 



It is well known that leaves are commonly drawn either by 

 the tip or petiole into the burrows of earthworms. According 

 to J. Jordan (22) the worms do not examine various parts of 

 the leaf as they were believed to do by previous observers, but 

 they catch hold of the leaf at any point and attempt to draw 

 it in. When leaves are seized by the side this attempt is usually 

 fruitless, and only in those cases in which the worm comes to 

 seize the leaf at some narrow part are the efforts of the creature 

 successful. In most of the previous experiments on this subject 

 the actual behavior of the worms was not witnessed, but Jordan 

 has based his conclusions upon observation of the activities of 

 the animals in weak light. 



H. Jordan (23) finds that neither the marginal sense organs 

 nor the margin ot the umbrella of the jelly-fish Rhizostoma are 

 necessary tor the production of rhythmical contractions. Cyanea 

 becomes more irritable to external stimuli after the margin of 

 the umbrella is removed; removal of the sense organs affects 

 the irritability of the animal but slightly. The author considers 

 that the nervous centers of the margin have the function of 

 regulating the reflex irritability of the animal. 



