22 BULLETIN 431, U. S. DEPARTMENT OF AGEICULTTJRE. 



through the stage described above as th-e third stage (figs. 7, 9, 

 17, and 18; PL II j, p). That the dead larvae are allowed to remain 

 in the cells often for weeks is in part the cause of the irregularity ob- 

 served in the appearance of the brood combs (p. 11). (Pis. I, IV.) 



APPEARANCE OF THE TISSUES OF A LARVA DEAD OF SACBROOD. 



The gross appearance of a larva during its decay after death from 

 sacbrood has just been described. The saclike appearance of the 

 remains, with its subcuticular watery-like fluid and its granular 

 content, can better be interpreted by knowing something of the 

 microscopic structure of the dead larva. 



A section through a larva (fig. 25, A) dead of sacbrood shows that 

 the fat tissue constitutes the greater portion of the bulk of the body. 

 The fat cells (FC) are coniparatively large. In the prepared section 

 when considerably magnified (C) they are seen to be irregular 

 in outHne, with an irregular-shaped nucleus (Nu). Bodies stained 

 black, more or less spherical in form and varying in size, are foimd 

 in them. The presence of these cells is the chief cause for the 

 granular appearance of the contents of larvae dead of sacbrood. This 

 appearance has often been observed by beekeepers and is a weU- 

 recognized symptom of sacbrood. 



In the section (A) may be seen a molt skin (Cg), which is at a con- 

 siderable distance from the hypodermis (Hyp). Another cuticula 

 (Ci) is already quite well formed and hes near the hypodermis. Be- 

 tween these two cuticulse (C2 and C^) during the earlier stages of 

 decay there is a considerable space ("intercuticular space") (IS). 

 This space is filled with a watery-looking fluid. That the fluid is not 

 water, but that it is of such a nature that a coagulum is formed in it 

 during the preparation of the tissues for study, is shown by the 

 presence of a coagulum in the sections. 



The body (B, A) wall of the larva is composed of the cuticula (C^), 

 the hypodermis (Hyp) and the basement membrane (BM). The 

 hypodermal cells may be present in the mass content of the larval 

 remains. These cells are comparatively small. Similar ones are to 

 be found in the tracheal waUs (Tra). These cells, however, make 

 up only a small portion of the contents of the sac. 



There are many other cellular elements to be foimd in the decaying 

 mass of larval tissues, some of which contribute to this granular ap- 

 pearance. Among these are the oenocytes (Oe), ceUs (D) larger than 

 the fat cel]s, but comparatively few in number. These are found 

 among the fat cells, especially in the ventral half of the body. The 

 oenocytes in the prepared tissues are irregular in outline, having a 

 nucleus regular in outhne. The cytoplasm is uniformly granular and 

 does not contain the black staining bodies found in the fat cells (C). 



