570 E. H. DUSHAM 



nature, and are therefore gland cells. Their secretion passes 

 to the exterior through very minute pores through the chitin 

 (fig. 7). These are evident only in very thin sections, cut ex- 

 actly perpendicular to the surface of the cuticula. Otherwise it 

 is almost impossible to make them out. With favorable sec- 

 tions they show as a fine streaking of the cuticula (fig. 10, p). 

 In portions of the cuticula stained black with osmic acid the 

 pores also show as minute white dots under an oil-immerson lens. 

 The secretion passes through these pores to the exterior and 

 without doubt spreads in a fine film over the outer surface of the 

 cuticula. 



NATURE OF THE SECRETION 



Mingazzini, in his work on Periplaneta orientalis, stated also 

 that these modified cells were glandular in function and probably 

 secreted an oily substance. So much did these cells resemble, 

 both in appearance and position, those cells in Apis, Trigona, 

 Bombus, Melepona, and Aphrophora, which were definitely 

 known to secrete wax, that it occurred to the writer that possibly 

 they might also perform this same function in the case of the 

 cockroach. Tests were accordingly made to see if wax was pres- 

 ent in these insects. A large number of the insects were cap- 

 tured and thrown into a bottle of wamied chloroform. After 

 remaining in this liquid for ten minutes, they were strained out 

 before the chlorofonn could have had time to have penetrated 

 into the interior of the insect and attacked the fat in the fat 

 cells. The chloroform was then filtered and divided into two 

 portions. From one of these portions the chloroform was entirely 

 evaporated on a water-bath. When the chloroform had been 

 entirely driven off, a brownish liquid was left which possessed 

 the characteristic cockroach odor and which, on cooling, solidified 

 into a greasy appearing substance. 



The next point was to find out whether this substance was 

 grease or a wax. It is well-known that fatty oils, or fats treated 

 with basic hydroxides, are decomposed into fatty acids and glyc- 

 erol, this decomposition being hastened by using alcohol as a 

 solvent for the alkali. Both the fatty acids and glycerol are 



