14 



layers beneath the top surface, there cannot be any freedom 

 of movement required for the female beetles to travel over 

 a large number of seeds and deposit their eggs; for eggs 

 cannot be crowded on a few seeds without the risk of ham- 

 pering the development of several, which, distributed over 

 a larger number of seeds, might have a better chance of 

 'completing their development. On the top surface, there is 

 no pressure of surrounding seeds but on the other hand com- 

 plete freedom of movement. 



To ascertain what exactly induces the beetles to come tO' 

 the top, the following experiment was conducted. A tin 

 box was filled with infested gram so as to leave no space 

 above the top surface for beetles to move freely and lay 

 their eggs. Into the tin six large holes were bored, four at 

 the side^ at right angles, one in the middle on the lid above 

 and one on the bottom below. Into each of these holes 

 a glass cylinder Fix inches long was fixed. All the cylinders 

 were filled with uninf ested gram for about half their lengthy 

 the seeds in the cylinder at the bottom being prevented 

 from falling by a paper disc fixed into it, with holes suffi- 

 ciently big for the beetles to pass through but too small 

 for the seeds (Fig. 8). This arrangement prevented the 

 possibility of any beetles emerging from the seeds inside 

 the cylinders themselves, but to make it absolutely certain, 

 the uninf ested seeds were made to extend inwards into the 

 tin for a little way from the cylinders. The cylinders were 

 then corked to prevent beetles from escaping. When the 

 arrangements were complete, the gram from the cylinderp 

 above and below A and D had a stiaight level but in the four 

 cyHndere at the sides it sloDed towardr the cork B, C, E and 

 F. It is clear that pressure is greatest on seeds in the bottom 

 cylinder D, less in the cyhnder on top A and least in 

 cyhndei-s B, C, E and F. On emergence of beetles inside, by 

 far the larger number worked their way into the top cylinder, 

 a few were found in each of the four cylinders at the sides,, 

 but none at all in the cyhnder below. " The beetles in two 

 of the side cylinders B and E. were now allowed to escape, 

 the grain was pressed back and kept at that level by means 

 of a paper disc with holes as in cyhnder D. The result was 

 that into these two beetles ceased to come uy while in the 

 other two C and F which were left as in th^ first exp'^ri- 

 ment, they continued to appear. When the paper discs 

 Were removed from the cylinders C and F and inserted in 

 B and E instead, the beetles put in their appearance in the 

 former but not in the latter. 



