BEHAVIOR OF THE LOWER INVERTEBRATES 411 



After excluding other theories, Kanda concludes that the stato- 

 cyst theory of geotropism is the most tenable. 



Kanda (21) has also studied the geotropism of Arenicola 

 larvae, subjected them to various salts solutions isotonic with 

 sea water and noted the influence of different media on the 

 sense of the response. Calcium and magnesium ions tend to 

 reverse the normally negative response, but their action tends 

 to be neutralized by sodium. The metallic ions are considered 

 to be the influential elements in reversing geotropism. The 

 usual positive phototaxis of the larvae may be reversed by the 

 addition of sodium chloride or potassium chloride, but the action 

 of these salts may be antagonized by calcium chloride or mag- 

 nesium chloride. 



In a paper on the biology of the snail (Helix) Kiihn (22) 

 treats of hibernation, loss of weight in winter, and reactions to 

 drought in summer. Helix can be made to come out of its 

 closed shell when placed under moist conditions. It does not 

 take dry food if its body does not contain a considerable amount 

 of water. 



The death feigning reflex of arthropods is described by Lohner 

 (23), who not only reviews a considerable amount of literature 

 on the subject but describes several experiments of his own 

 on different species of diplopods. 'The destruction of the brain 

 or decapitation makes the reaction much more difficult to elicit, 

 but these operations do not destroy it entirely. If the nerve 

 cord is cut the part anterior to the cut can be made to perform 

 this reflex. The reflex is not shown by an isolated part of the 

 body behind the fifth segment. 



The reactions of Bursaria to food and the processes of diges- 

 tion in this species have been carefully studied by Lund (24). 

 Bursaria may reject certain kinds of solid materials while it 

 takes in others, depending on the action of the ciliary mechanism 

 of the oral cavity. Large particles either do not enter the oral 

 sinus or are rejected before reaching the latter, while small 

 particles may be carried into the deepest part of the sinus and 

 then carried out in a stream which passes backward on the 

 ventral side of the body. The amount and rate of food taking 

 depends on the condition of the animal. Bursaria appears to 

 have a faculty analagous to the sense of taste, as it rejects food 



