20 



BULLETIN 431, U. S. DEPARTMENT OF AGRICULTURE. 



third. The effect of the drying on this third is quite perceptible also. 

 The surface markings and notched margin of the normal larva are 

 still indicated in the decaying remains, but are much less pronounced. 

 The subcuticular fluid is no longer in evidence. 



CoTisistency of the contents of the sac. — ^Upon tearing the sac, the 

 contents are found to be less fluid than in preceding stages. The 

 decaying tissue mass is still granular in appearance. As the drying 



Fig. 22.— Fifth stage: Scale, or larval re- 

 mains, in sacbrood as seen on lookiag 

 into the cell. (Original.) 



proceeds further the contents of the 

 sac become pastelike in consistency. 

 ■ Condition of the virus in the fourth 

 stage. — As in the preceding stage, the 

 larval remains in the fourth stage do 

 not seem to be infectious. 



Fifth Stage. 



Fig. 23.— Fifth stage: Scale, or larval remains, 

 in sacbrood viewed at an angle from above. 

 (Original.) 



The dead larva in this last stage 

 has lost by evaporation all of its 

 moisture, leaving the dry, mummylike remains know^n as the "scale." 



Anterior third. — The anterior third (fig. 22 ; PI. II, Z) through dry- 

 ing is retracted from the mouth of the cell, with the apex drawn stiU 

 deeper into the ceU and raised toward its roof. This third is greatly 

 wrinkled, and, being of a very dark-brown color, presents often an 

 almost black appearance. 



Middle third.—Tlie middle third (fig. 23; PI. II, r), is deeply 

 concave from side to side and may show remnants of the segmental 

 markings of the larva. The surface is often roughened through 

 drying. Sometimes both longitudinal and transverse tracheae are 



