Hadley, Behavior of the American Lobster. 289 



toward the dark areas (areas of non-stimulation); the other to 

 move in the direction of the longitudinal axis of the body either 

 toward or from the source of light. Were we dependent upon 

 such experiments as these for our belief in the existence of a sep- 

 arate response to light-intensity, regardless of directive influence 

 of light, we might well say that the photopathic and phototactic 

 responses are, in the end, one and the same. But the writer has 

 adduced in the previous section other data which separate more 

 clearly these two types of reaction. 



VII. ANALYSIS. 



It has for some time been the custom to state that certain organ- 

 isms are positively phototactic or positively photopathic, and that 

 other organisms are negatively so. The index of reaction for 

 several crustaceans has been so recorded, but the observations 

 are usually incomplete, often uncritical, and sometimes of ques- 

 tionable significance. It is true that, in a very general way, organ- 

 isms react positively or negatively to light. For instance, it may 

 be said that the lobster shuns the light, that Palemonetes is attracted 

 by the light, and that the larvae of Limulus avoid the Hght. The 

 definite statement, however, that the larvae of Limulus are 

 negatively heliotropic, or that Palemonetes and larvae of Homarus 

 are positively phototactic, is as inadequate as would be a biography 

 written on the basis of a single day's association with a human indi- 

 vidual. It may be true that by the time the adult stage is reached, 

 the reactions of many animals have become more or less stereo- 

 typed, so that reactions like those of the moth to the flame, are 

 easily predictable. In the larval and adolescent stages, on the 

 other hand, the reactions are frequently more variable. To say 

 that the lobster of the second larval stage is positively phototac- 

 tic or positively photopathic is, as has been demonstrated, by no 

 means a correct interpretation of the facts of the case, for slight 

 changes in the conditions of stimulation may be sufficient to 

 reverse the index of reaction. This variability doubtless occurs in 

 many arthropods. It thus becomes evident that, although the 

 young lobsters may be regarded as machines upon which many 

 diff^erent external forces act and cause certain reactions, still 

 (except for the definite body-orientations which are invariably 

 determined by the directive influence of the light rays) they are 



