Centrifugal Force upon Beetles^ -^SS^ 5^^ 



a leaf and clings to its under surface. The tip of the abdomen 

 moves rhythmically up and down about fifteen times at intervals 

 of a little less than one second. This results in the exudation of a 

 drop of viscid, colorless fluid about one-third the transverse 

 diameter of the egg. The egg is forced out a moment later and 

 carries with it this drop of fluid by means of which it is fastened to 

 the leaf. When the egg reaches the leaf it is pushed back away 

 from the beetle (Fig. i), which then moves to one side and again 

 begins the rhythmical movements which precede the laying of 

 another egg. In this way eggs are laid in a double row as shown 

 in the accompanying figure (Fig. 2), but frequently three or more 

 may be laid in one row. The intervals between the layings of the 

 individual eggs average one minute and twenty seconds" (Hegner 

 '08 a). Two to nineteen eggs are laid at one time, the average 

 number being eight. Fig. i indicates the orientation of the egg 

 of C. bigsbyana lying in the ovary and also the final position after 

 it has been laid. 



IV THE EFFECTS OF GRAVITY UPON THE DEVELOPMENT OF THE 



EGGS OF INSECTS 



That the position of the insect egg after laying has no influence 

 upon the development of the embryo was proved by Wheeler 

 (1889) in the case of Blatta. This author kept capsules from 

 fourteen to twenty days in the following positions: 



" I Resting with the lateral faces perpendicular and crista 

 uppermost. 



"2 Resting on the crista with the lateral faces perpendicular. 



"3 Resting on the left lateral face. 



"4 Resting perpendicularly on the anterior end. 



"5 Resting perpendicularly on the posterior end. 



"In all these cases the eggs developed normally, without the 

 slightest indication of displacement in position or alteration of 

 shape in the embryo; whether they were forced to develop with 

 their heads pointing up or down." The conclusion reached was 

 that "the force of gravitation has no perceptible efi^ect on the 

 development of the eggs of Blatta 



