8 Transactions of the Society. 



vessel in diameter and capacity ; it is often as large as, or larger than, 

 either the colon or rectum. From this chamber a second narrow 

 portion {inv^), which is considerably longer than the first, but not so 

 sharply defined, leads to a lateral enlargement slightly constricted in 

 the middle (w v'^) ; this portion is in shape like two elongated pyri- 

 form organs with their larger ends together and fusing ; but, of course, 

 the lumen is continuous. From this enlarged lateral portion another 

 narrow part (mv^) of the vessel, much longer than the previous 

 narrow parts, and more undulated, runs forward nearly to the articu- 

 lation of the second leg. Up to this point the Malpighian vessel has 

 been placed at the side of, or slightly under, the ventriculus : the 

 extent to which it passes under varies in different specimens, and 

 probably in the same specimen at different times, depending on the 

 relative distension of the canal and the Malpighian vessels respec- 

 tively, and on the precise form and position of the latter, which are 

 not by any means constant. After attaining the point to which it 

 has been described, viz. about the articulation of the second leg, the 

 course of the vessel entirely changes ; it turns sharply upward and 

 then backward, so that it folds over the anterior edge of the ven- 

 triculus, and the remainder of the vessel is a reflexed portion (to v^), 

 which lies upon the ventriculus and runs straight backward. It 

 gradually enlarges towards its distal end, which is blind and rounded 

 {m v^). A powerful fasciculus cf muscles (in) which arise from the 

 sides and dorsal cuticle, are inserted by tendinous attachments into 

 the wall of the vessel just behind the lateral enlargement, and probably 

 assist in the peristaltic movements. The vessel is also attached to 

 the side of the body at m}, but in this case apparently merely as a tie, 

 not by muscles of any importance. The peristaltic movements and 

 the transfer of excretory matter, of course, proceed from the blind end 

 of the vessel toward the rectum, and are stronger than those of the 

 canal ; this is usual in the Oamasidse, but the movement is not so 

 strong as in Dermanyssus, and many other members of the family. 

 The Malpighian vessels are generally more or less distinctly seen 

 through the dorsal shield in living specimens, and are the most con- 

 spicuous organs in the body ; they are equally conspicuous in the 

 nymphs and larvae, and may even be clearly seen in the advanced 

 embryo while still within the egg, and at that early period they are 

 already filled with the white matter. 



The Eeproductive Organs. 



This system is another of those which bears a strong resem- 

 blance to that of the Orihatidse, but naturally there are difierences of 

 considerable importance, as will be seen in the following description. 



As in most other families of the Aearina, these organs, during the 

 period of activity and maturity, are extremely large in proportion to 

 the whole size of the creature ; so much so that they often appear to 

 push all the other organs out of place ; this, as might be anticipated, 

 is more especially the case with the female when the eggs are ripe. 



