512 R. W. Hegner 



Wheeler also proved that the antero-posterior differentiation of 

 the embryo of Leptinotarsa decemhneata is not affected by changes 

 in the position of the egg after laying, but is predetermined in the 

 ovary. 



During the course of my work with Calligrapha, eggs were taken 

 as soon as laid and placed in every possible position. The embryos 

 were found to be in no way affected by the orientation of the egg 

 with respect to gravity. 



The only exception to the rule that gravity has no influence upon 

 the development of insects' eggs seems to be that of Hydrophilus 

 aterrimus reported by Megusar ('06). The eggs of this water 

 beetle are laid in a boat-like cocoon which is kept in an upright 

 position in the water by means of a peculiar mast. Megusar 

 found that if these cocoons were inverted, thus also inverting the 

 eggs within, the development of the eggs was retarded and a 

 deformity in the embryos resulted. The small number of larvae 

 that hatched lived for only a short time. 



V A BRIEF ACCOUNT OF THE NORMAL EMBRYONIC DEVELOPMENT 

 OF CALLIGRAPHA BIGSBYANA 



Eggs that have just been laid contain polar bodies in various 

 phases of formation; these are given off into a thickening of the 

 " Keimhautblastem" at a point slightly anterior to the median 

 transverse axis of the egg. The female pronucleus lies in an 

 amoeboid accumulation of cytoplasm among the yolk-globules. 

 It moves inward and conjugates with the male pronucleus at a 

 point level with the polar bodies. Here the first cleavage divisions 

 take place. As cleavage progresses a separation of the nuclei 

 into two sections occurs. The nuclei of one group form a more or 

 less regular layer equidistant from the periphery; these pre- 

 blastodermic nuclei (Fig. 17, pbl. n) move outward and fuse 

 with the "Keimhautblastem." Cell walls now appear for the 

 first time and a blastoderm is formed of a single layer of regularly 

 arranged cells. The nuclei of the other group (vitellophags), 

 remain behind scattered throughout the yolk (Fig. ij, vt). Eight 

 of the nuclei that reach the posterior end of the egg do not remain 



