Pearl, Reactions of Limulus. 159 



ever part of the body is stimulated. The reactions to very 

 weak tactile stimuli applied to the tips of the chelae have been 

 described above (p. 155). 



The characteristic gustatory reflexes of the adult Liundus 

 (cf. Patten, '93) I have not been able to induce in embryos of 

 the "trilobite" stage. Repeated experiments were made on 

 this point with the substances which produced prompt and 

 strong chewing movements in the adult, but always with nega- 

 tive results. No distinct reactions of the legs are produced 

 when clam juice is dropped on the coxal joints. The absence 

 of these reflexes is probably correlated with non-development 

 of the sense organs which are stimulated by edible substances. 



The adult animal is very sensitive to weak thermal stimuli, 

 responding promptly and in a characteristic way to a puff of 

 warm air, or to the warmth of the hand laid on the margin of 

 the carapace (cf. Patten, '93). The embryos fail to show this 

 sensitiveness to thermal stimulation. They will only respond 

 to a strong temperature stimulus such as is given by holding a 

 red-hot needle very close to the body, and then the reaction is 

 a general one, like that given in response to tactile stimulation. 

 The absence of characteristic temperature reflexes is again prob- 

 ably to be explained as due to the non-development of the 

 proper sense organs at this stage. 



Several years ago Loeb ('93) gave a brief account of the 

 reactions of Limulus embryos in the "trilobite" stage to light. 

 The essential results of this author's work are given in the fol- 

 lowing sentences (loc. cit., pp. 98-99). (i) "Die Larven von 

 Lirmiliis polyphemus sind nach dem ausschKipfen auf dem Ei 

 positiv, spater negativ heliotropisch. " (2) "Die positiv helio- 

 tropischen Bevvegungen werden stets schwimmend, die negativ 

 heliotropischen stets kriechend ausgefiihrt." Throughout the 

 course of the present work considerable attention was paid to 

 the subject of phototaxis, and a large number of experiments 

 along this line were performed. It very soon appeared that 

 there were other factors present in the reactions to light, be- 

 sides those enumerated by Loeb. The case is not by any 

 means as simple as his account would indicate. The conditions 



