84 B1UT1SH TYEOGLYPHID^. 



of the vas deferens diminishes gradually as it approaches 

 its distal end. The tunica propria of this duct is 

 stronger than that of the testis, but there is not any 

 muscular tunic. The two vasa deferentia are of equal 

 length, but in Tyroglypfww longior JSTalepa found that 

 in consequence of the more forward position of one 

 testis than of the other the vasa deferentia were of 

 unequal length. I am not aware that any other author 

 has traced the course of these organs, for Haller's 

 PL X, fig. 9, af , although called the duct from the 

 third testis, is evidently the duct from the accessory 

 gland. 



The Ductus Ejaculatorius. This in Glycyphagus 

 platygaster is a short duct (PL B, figs. 5, 6, d e) formed 

 by the joining of the two vasa deferentia (fig. 5, v d) ; it 

 passes through a hole in the chitinous supporting-piece 

 of the penis, and on its distal side widens out to form a 

 distensible chamber (dec) ; which collapses when not in 

 action (fig. 6, dec), forming a wide fold, and is only 

 distended and functional at the time of ejection of the 

 genital products. This enlarged chamber, or something 

 of a similar nature, was seen by Nalepa in Tyroglyphus 

 longior. At first he took it for a separate vesicula 

 seminis, but in the second part of his paper he corrects 

 this and says he has ascertained that it is merely an 

 enlargement of the ductus ejaculatorius. He found a 

 muscular tunic to this portion of the ductus. 



The Accessory Glands are far the largest organs in 

 the male genitalia ; this is quite usual in the Acarina, 

 but the variation of them in different families and 

 genera, and even in different species, is very great. 

 The opportunities of variation are not so numerous in 

 the Tyroglyphidse, whose genital organs so far as they 

 are known are comparatively simple, as they are in 

 the far more complicated organs of the higher Acari, 

 such as Bdella, etc. 



In Glycyphagus platygaster there are two great acces- 

 sory glands, which, however, cannot be considered as 

 paired ; they differ in form, size, and structure. One, 



