436 PROCEEDINGS OF THE AMERICAN ACADEMY. 



and Hesse ('98^". p. 459) have noted, with the ventral side uppermost 

 and always with the anterior end higher than the posterior. This 

 relation of the two ends might be supposed to be due to the need of 

 having the anterior end in clear water, and therefore to be a reaction 

 to the water and sand in the surroundings and not directly to gravity, 

 but that this assumption is false is seen from the following experi- 

 ments. If several amphioxus are placed in a closed box made of 

 coarse wire gauze and filled with sand and the whole immersed in 

 sea water, in a few hours they will be found at the top of the sand with 

 their anterior ends projecting into the sea water. If now the box is 

 cautiously inverted, some of the animals will keep their original 

 positions, and thus their anterior ends will project from the under side 

 of the box into the adjacent sea water ; but they will remain here only 

 a short time, for sooner or later they wiU make their way upward 

 through the sand to the top. In a similar way if, after they have 

 come to rest at the top, the box is rotated through a quadrant so that 

 their anterior ends project sidewise into the sea water, they will again 

 desert this position and move to the top. Further, if in a funnel 

 whose stem has been broken off short an amphioxus is buried in sand 

 in such a way that its anterior end projects downward out of the small 

 end of the funnel into the sea water, it will leave this lower end and 

 make its way upward through the sand to the top, even if, in doing 

 so, it emerges on sand above the level of the water. It is therefore 

 evident that amphioxus will come to rest in the sand only when its 

 anterior end is above its posterior one, and, from the conditions under 

 which this occurs, such responses seem to be strictly geotropic. 



5. Chemical Stimulation. 



The chemical sense of amphioxus, as remarked by Nagel ('94^ p. 192), 

 is not unlike that of a worm in that its seat is the whole outer surface 

 of the animal and not simply the region around the mouth. This 

 sense is doubtless serviceable chiefly as a means toward escape from 

 unfavorable chemical surroundings and probably has little or nothing 

 to do with the direct feeding habits of the animal. As is well known, 

 amphioxus does not seek its food, but takes what is brought to it in 

 water currents, selecting from this supply only in the crudest fashion, 

 if in fact it can be said to select at all. Nagel ('94b, p. 58) has shown 

 that the outer surface of amphioxus is sensitive to chloroform, etc., 

 and declares that, notwithstanding the presence of the so-called 

 olfactory pit near the anterior end, one part of the animal's body is 

 about as sensitive to chemical stimulation as another, though the tail 

 may possibly be more sensitive than any other portion. 



