WALTER E. GARREY 117^ 



muscles. Such a detailed study is beside the purpose, and beyond the 

 scope of this communication; a brief reference will suffice. Blacken- 

 ing one eye of positively heliotropic insects decreases the tonus and 

 weakens the extensors of the opposite side, resulting in a flexion of the 

 legs due to the unopposed action of the flexors. There is then at least 

 a partial crossing of extensor nerve paths. The condition is similar 

 to that demonstrated by operative methods on Gelasimus pugnax 

 by Loeb and Maxwell.^^ The nerve paths between the eye and the 

 flexors are not crossed; thus blackening one eye decreases the tonus 

 and weakens the flexors on the same side and extension is unopposed. 

 With the upper halves of the eyes blackened, the tonus of dorsal 

 muscles is decreased and the extensors of the anterior legs are princi- 

 pally weakened with resulting flexion. Loss of function of the lower 

 part of the eye weakens the flexors of the anterior legs, which become 

 extended by the unopposed extensors, while the loss of tonus of the 

 ventral body muscles results in opisthotonus. Other relations are 

 easily made out. 



Masked Conditions of Tonus. — The truest gauge of the physio- 

 logical condition of a muscle is to be found in the character of its 

 responses. The circus motions, which result from blackening one 

 eye, are the result of asymmetrical conditions of the tonus of muscles 

 of the two sides; these conditions exist in the resting muscle as is 

 indicated by the resting postures. It often happens however that 

 these resting postures are not in evidence, especially if the difference 

 in illumination of the two eyes is not great, or in faint illumination 

 after one eye has been blackened. Postures seen in one form may 

 rarely if ever be evident in another; for example, the lateral bending of 

 the abdomen of Proctacanthus often is not evident under ordinary 

 illumination after one eye is covered. Activity however unmasks 

 the true state of the muscle. Thus a sharp blow on the table, touching 

 the insect with a bristle anywhere on the body, or a gentle blast of 

 air delivered from any angle, ehcits a general contraction of the body 

 muscles without any progressive movement. In this response the 

 expected postures are always assumed, at least momentarily; for 

 example, a lateral bending of the abdomen of Proctacanthus always 



" Loeb and Maxwell,^^ p. 134. 



