158 Journal of Comparative Neurology and Psychology. 



will start the burrowing ; a small pebble or a few projecting 

 sand grains in the path produce the same result. 



The burrowing reaction is then evidently started primarily 

 as a result of the strong positive thigmotaxis of the margin of 

 the cephathorax. This thigmotactic tendency is so pronounced 

 that the mere catching of the anterior margin of the cephalo- 

 thorax on a few sand grains is sufficient to start the animal 

 pushing ahead into the sand. I have frequently seen the bur- 

 rowing started in this way. 



The reflex nature of the burrowing reaction is well shown 

 in some cases I have observed in which an embryo which had 

 started burrowing and had succeeded in burying perhaps half 

 the body, would, by the violence and lack of good coordina- 

 tion of the leg movements, accidentally lift the anterior end out 

 the hole which it had excavated. Such individuals, in every 

 case observed, did not return to the burrowing but walked off 

 over the sand in whatever direction they were pointed, until 

 they chanced again to get the anterior margin of the margin of 

 the body caught by some obstruction. 



Complex Reflexes. — During the stage of development un- 

 der consideration the "gill scraping" reflexes of the sixth legs 

 appear. These consist in complete extensions and flexions of 

 the sixth legs with the surface of the abdominal appendages. 

 The reflex is a very characteristic one and its apparent purpose 

 is to free the outer surface of the gills of any material which 

 might prove injurious. These movements appear at once in 

 their perfect form, so far as I have been able to observe. There 

 is no process of gradual perfection by practice, or learning. 

 The action is performed for the first time by the embryo in 

 quite the same manner that it is by the adult. 



Reactions to Stiinuli. — The reaction of embryos in the "tri- 

 lobite" stage to tactile stimuli of all but the weakest intensities 

 is precisely the same as that described above for the preceding 

 stage. It consists in a strong contraction of all the flexor mus- 

 cles of the body. This state of contraction persists as long as 

 stimulation is continued. There are no differentiated responses 

 to localized tactile stimuli. The same effect is produced what- 



