THE BRITISH WOODLICE. 



49 



Fore-gut 



FIG. 32. — EMBRYO OF THE WOODLOUSE SHOWING THE 



THREE DIVISIONS OF THE INTESTINE SEPARATELY 



DEVELOPED {PoVCellio SCClber). AFTER ROULE. 



appendages have made their appearance and the mesoderm, 

 (which has grown considerably, to form the beginnings of the 

 muscles) has sent prolongations into each of them. About this 

 time, spaces (see fig. 31) are formed in the muscular mesoderm 

 which are all that remain of the true body cavity characteristic of 

 animals above the level of the jelly- fish, and in these spaces 



the blood ultimately cir- 

 ///^-y^^^^^^s^ culates. 



The body next alters 

 somewhat in shape and 

 the three divisions of the 

 intestine approach one 

 another (see fig. 32) 

 previous to their junction. 

 As may be imagined dur- 

 ing these processes the 

 food-yolk has gradually 

 been used up and the 

 space which it occupied 

 taken by the internal 

 organs, which we have 

 mentioned. 



In the last stages of 

 the development the ap- 

 pendages become larger 

 still, the heart makes its 

 appearance, segmentation 

 of the body is completed, 

 and except that the 

 seventh pair of walking 

 legs are as yet rudimen- 

 tary the woodlouse is 

 completed. It is only 

 after hatching that the 

 pair of legs mentioned, attain to their normal length. 



The process of segmentation of the egg and the formation of 

 its layers lasts about a fortnight, while the completion of the 

 development proceeds much more rapidly, for another three 

 weeks bring it to an end. 



After the first moult or change of skin the last pair of 



-ffeazt 



'erlicafam. 



fo /V777L 



dtyeslti>e pkmds 



FIG. 33.- EMBRYO OF THE WOODLOUSE SHOWING TRACES 

 OF THE SEGMENTS (PorcelHo SCClber). AFTER ROULE. 



gland, 



•Inieslme 



FIG. 34. — AN EMBRYO WOODLOUSE READY TO BE 



hatched (PorcelHo scaber). after roule. 



