PHYLUM ARTHROPODA 



323 



Ov 



queens or workers. Unfertilized eggs are usually laid in drone 

 cells, and those that develop become drones. How fertilization 

 is controlled is still 

 unknown. 



The egg undergoes 

 superficial cleavage 

 (p. 86, Fig" 50, D) as 

 in the crayfish (p. 289). 

 A blastoderm of a single 

 layer of cells is formed 

 at the surface ; this 

 soon thickens on the 

 ventral side, forming 

 a germ band. The 

 germ band segments, 

 sends out protrusions 

 which become append- 

 ages, and grows until it 

 completely surrounds 

 the egg. In three days 

 the larva emerges from 

 the egg-shell. 



The changes that 

 take place in an insect 

 during its growth con- ^^ 



Stitute its metamor- gland; AGID, duct of acid gland; BGl, alkaline 



-hh ' TVi Pf i7~ &land ; Ov, ovary ; ov, ovarian tubules ; OvD, 



j?ftfliW>i - oviduct; PsnSc, poison sac; Spm, spermatheca; 



tory of an individual Stn, sting; StnPlp, sting feeler; Vag, vagina. 



bee may be divided 

 into four periods 

 (Fig. 247): (i) egg, (2) larva (FZ,. 51,), (3) pupa (N}. U) adult 

 or imago (Fig. 236). When the larva hatches, it lies at the 

 base of the cell (Fig. 247, FL), floating in the food prepared by 

 the workers and known as chyle or " bee milk." Chyle is com- 

 posed of digested honey and pollen, probably mixed with a 





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