192 S. O. MAST. 



and put into a glass jar containing water 20 cm. deep. They all 

 soon reached the bottom, but there was not the slightest evidence 

 of swimming downward. They did not orient and the longitudi- 

 nal axis was nearly horizontal in many of them. In fact there 

 was but little bending and twisting in the larvae. Most of them 

 remained perfectly quiet as they sank to the bottom and none 

 of them deflected more than 2 cm. from the vertical. The same 

 was true for larvae approximately i cm. and 1.6 cm. long taken 

 from the carrion and put directly into the water on the second 

 and fifth days following. But in case of other specimens which 

 were kept in a dish without food for several hours before they 

 were put into the water many did not sink. This was due to 

 the formation of small bubbles of gas near the anterior end. 



Some of the larvae which had thus been without food were 

 killed in boiling water, others in alcohol. Of the dead speci- 

 mens some sank, others floated. The dead ones were now 

 mixed with living ones, and all put into a small glass jar con- 

 taining water 80 cm. deep. After the larvae which were heavier 

 than water had sunk to the bottom, the jar with the upper 

 end closed was suddenly inverted. Those which had been at 

 the bottom sank again, while those which had been at the top 

 rose. In both lots there were some living and some dead 

 specimens, but it was only with great difhculty that one could 

 .distinguish them. In nearly all specimens the axis was approxi- 

 mately horizontal. There was no evidence whatever of a swim- 

 ming movement in any of them. If there is no gas in them they 

 sink to the bottom where they crawl about much as they do in 

 air. If they contain bubbles of gas they float at the surface, 

 where in one instance they were observed to remain alive more 

 than twenty-four hours. 



It must therefore be concluded that blow-fly larvae do not 



react to gravity, either in water or out of it. In air they may be 



found to orient and crawl nearly straight upward on objects, 



but this is not due to a response to gravity on the part of the 



organisms. In water they sink to the bottom or float at the 



top, depending upon the amount of gas they contain, but there 



is no evidence whatever indicating that they can swim. 



GoucHER College, 

 Baltimore, Md. 



