340 



THE LIFE-HISTORY OF HYDROBIUS FUSOIPES, L. 



Fig. 22. Ventral view of same embryo. 



Figs. 23 and 24. Lateral and ventral views of the 9th day stage showing the ventral curvature of the 

 enil>i 



Fig. 25. 10 days stage showing the segmentation of the appendages and the commencement of the 

 formation of the lateral tracheal trunks (tr.). 



Fig. 26. 11 days stage. The first sign of the heart (Id.) and of the muscular system. 



Fig. 27. 12 days stage. The pigmentation of the lateral tracheal trunks. 



Fig. 28. 13 days stage. The building up of the tracheal system. 



Fig. 29. The 14th day, some hours before the embryo is to emerge. Note the amount of free space 

 within the shell. 



Figs. 30 and 31. The same egg shortly before and within a few minutes of the escape of the embryo. 

 p.o., pulsating organ. The tracheal papillae ("setose gills") of the second thoracic and first abdominal 

 segments are seen in fig. 30, and all these are visible in fig. 31. Note the tightly packed embryo in fig. 31. 



Figs. 32 and 33. The right and left mandibles of the imago seen from above. 



Fig. 34. The right antenna of the <$ of the imago. 



