Salivary Glands 69 



histologist. A full-grown larva is decapitated on a glass 

 slip. The glands often float out with the blood ; if this 

 docs not happen, gentle pressure should be applied. The 

 tissue may be examined at once, while still bathed in the 

 blood of the insect, but the finer details cannot be made 

 out until the glands are stained. The cells do not take 

 the stain until they are killed, and it is instructive to 

 note that they remain long unstained in non-poisonous, 

 aqueous, staining fluids. Strong alcohol or osmic acid 

 (the latter is preferable) hills the cells, and then the stain 

 penetrates. The following procedure will be found to 

 answer well : — Immerse a gland momentarily in a mixture 

 of equal parts of 1/^ solutions of osmic and acetic acids, 

 wash in distilled water, stain with acetized methyl green, 

 followed by carmine, and mount in glycerine. The 

 nuclei vary much in shape, being circular, oval, club- 

 shaped, &c. Sometimes they send out radiating projec- 

 tions into the cell-protoplasm. They slowly change their 

 figure. Each nucleus contains one or two nucleoli, 

 besides a long convoluted, transversely striated cord. 

 The ends of the cord are attached to the nucleolus (one 

 to each,- if there are two nucleoli). The transverse 

 striation of the cord suggests that it is composed of a 

 number of component disks, which are sometimes seen 

 separated into small groups in a broken-up nucleus. 

 Korschelt ^ believes, however, that the striation is due to 

 infolding of the surface. He considers that Balbiani's 

 figure is too regular. The nucleoli diifer much in shape, 

 being cup-shaped, oval, lobed, &c. They do not stain 

 with acetized methyl green, though they readily take a 

 carmine stain. The cord stains with methyl green, but 

 very feebly with carmine. 



Similar nuclei have been found in the Malpighian 

 tubules, as well as in the epithelium of the stomach and 



' Zool. ^w,?.,vii, pp. 189. 221.241 (1884). 



