520 MEDICAL ENTOMOLOGY 



The second follicle is usually distinctly separated from the first by 

 a constriction, and is elongate and slightly narrowed in its middle. The 

 lower half contains the nucleus of the ovum, with a considerable amount 

 of granular material, while in the upper half there is a mass of nutritive 

 cells, many of which are cylindrical and directed axially towards the 

 growing ovum. At the upper end of the second follicle there is a small 

 cluster of minute undifferentiated cells, the germarium, from which 

 future follicles will be developed ; from the upper end of this the usual 

 apical thread passes forwards to the dorsal region of the anterior end of 

 the abdomen. 



The organ of Berlese (Plate LXV, fig. 6) is a small round body of 

 a dull white colour, lying on the right side of the ventral region of the 



abdomen, immediately above the incision in the ventral 

 The organ of Berlese . 



margin of the fourth segment. It is closely adherent 



to the integument, but is free from the internal organs, the scanty 

 supply of tracheae which it receives being insufficient to bind it down 

 to them. No duct can be found running between it and the ovaries, 

 though they are' supplied with tracheae from a common stem, a branch 

 of which might easily be mistaken for a duct. At the place at 

 which it is attached to the integument there is a small oval plate of 

 chitin in the membrane between the fourth and fifth sternites, and in 

 the centre of this is a minute aperture, guarded by extremely fine 

 spines. From this aperture a chitinous duct leads into the interior of 

 the organ. The substance of the organ is composed of a mass of round 

 cells arranged around a small central space, the extent of the lumen 

 varying a good deal in different conditions. The whole structure is 

 surrounded by a very thin but definite capsule. No aperture leading 

 from the chitinous duct to the central space has been found, but 

 there is strong reason to believe that it exists. The cells immediately 

 surrounding the duct are smaller and more cylindrical than those which 

 make up the rest of the organ, and have different staining reactions. In 

 one of Berlese's figures the central portion surrounding the duct is 

 referred to as the organ of Ribaga. 



The appearance of the organ on section differs very greatly in different 

 cases, from causes which cannot as yet be explained. The cells may 

 be more or less uniform in arrangement and in shape throughout 

 the organ, or they may be more densely packed and smaller in one 

 part than in another ; in some parts they may be degenerated and 

 apparently replaced by a finely granular mass, or practically all the 

 cells may be enlarged and vacuolated. Since no satisfactory 



