INTERNAL ANATOMY. 79 



seen they are round, about 7 ^ in diameter, and fre- 

 quently present several nucleoli. 



The Salivary Glands (PL A, figs. 6, 7). These glands 

 are always known by this name in the Acari ; it prob- 

 ably expresses their principal function, but I have 

 elsewhere expressed a doubt whether it is absolutely a 

 correct name. Grudden * calls them the salivary or 

 poison-glands. There is not, however, any reason to 

 suppose that the Tyroglyphidae, which are vegetable 

 feeders, require or possess poison-glands, although such 

 a suggestion might readily be entertained with regard to 

 the predatory families such as the Trombididae. In 

 Trombidium and Bdella, and also in the Hydrachnidaa, 

 these glands assume great variety and importance. I 

 have treated elsewhere of them fully with regard to these 

 forms, and with regard to the views taken by different 

 authors concerning them.f In such few Tyroglyphida? 

 as have been studied in this respect these glands are far 

 smaller and simpler than in the great group of which 

 Trombidium may be considered to be a type ; in Glyct/- 

 phagus platygaster the glands consist of two on each 

 side of the body, lying close together at the side of the 

 anterior part of the cephalothorax. Each of these 

 glands is paired with its fellow on the other side of 

 the body, but the two on the same side, although 

 histologically similar, are very different in size. No 

 one who is well acquainted with the salivary glands of 

 the Trombididas, etc., can doubt that the two pairs of 

 glands above spoken of in G. platygaster are analogous. 

 The larger of the two (PL A, fig. 6) is a flattened, 

 slightly kidney-shaped gland consisting of very large, 

 almost triangular, secreting cells almost radiating from 

 a centre ; they have an average length, in the radial 

 direction, of about 40 n to 50 p, and an extreme 

 width of about 30 ILL ; they have conspicuous round 

 or elliptical nuclei of about 10 ju in diameter, which 



* Loc. cit., p. 12, pi. ii, fig. 8. 



f " The Internal Anatomy of Thyas petrophilus" loc. cit., p. 188. 

 ' The Internal Anatomy of Bdella" loc. cit., p. 492. 



