78 BRITISH TYROGLYPHID^E. 



When the Acari are mounted in Canada balsam 

 these concretions do not depolarize light. 



The cells near the distal ends of the caeca in G-lycy- 

 pliagus platygaster are usually thicker than those of the 

 ventriculus itself ; they have clear nuclei and nucleoli. 

 The exhausted cells found in the lumen of the caeca 

 before they collapse have an average diameter of about 

 20 /LI. Berlese has figured the cells of the caeca of 

 Hisliostoma rostro-serratum practically similarly.* 



The cells of the colon in Glycyphagus platygaster differ 

 somewhat at the two ends of the viscus ; those at the 

 anterior end are flattish cells, somewhat of the nature 

 of pavement epithelium; they average about 19ju in 

 diameter by a thickness of about 6 /* ; those at the 

 posterior end are smaller but thicker. They have an 

 average diameter of about 13 /u, and are about as thick 

 as their diameter ; all have round nuclei of about 4 p 

 to 5 fj. diameter, and are distinctly nucleated. Nalepa 

 says that the cells of the colon of Tyroglyphus longior 

 are flat and small. The colon does not contain clavate 

 cells. 



The cells of the extreme anterior part of the Rectum 

 of Glycyphagus platygaster are clavate ; those of the 

 remainder have a length of about 24 ^ and a thickness 

 of about 10 ft. Nalepa says that in Tyroglyphus longior 

 the upper part of the rectum is lined with columnar 

 cells whose secretory functions are unmistakable, and 

 that they gradually fade into a small-celled epithelium 

 which clothes the lower portion of the rectum and is 

 covered by a soft cuticula ; he also says that the clavate 

 cells have small nuclei surrounded by a space (Secre- 

 traum ?), and that they are not like fat-cells. 



Nalepa states that the Malpighian vessels of T. 

 longior have a wall of a soft structureless membrane 

 and a lining of large round secretory cells with spaces 

 between, that they project into the lumen, and are 

 usually filled with finely-granular colourless matter, 

 and that the nuclei cannot usually be seen : when 



* " Ricerche sulli Organi, etc.," loc. cit., fig. 22. 



