ES^TERNAL ANATOMY OF THE GAMASID.E. 311 



Malpighian vessels which are usually free are attached to the hind caeca of the ven- 

 triculus almost the whole lenyth of the ca3ca. 



Excretory Organs. 



In addition to the great Malphigian vessels there exist in some Garaasids, although 

 apparently not in all, a pair of organs which I believe have not yet been recorded in the 

 family ; they lie in the side of the hinder part of the abdomen close under the skin, 

 and are stout sacs discharging to the exterior by a pore in the cuticle. In Jlcemo- 

 gamasus horrldits there are two such sacs on each side; they are flattened and the two 

 are close together (PL XXXII. fig. 22). They have been practically similar in the other 

 cases where I have found them. These organs are well known in other Acarina, e.g. in 

 the Tyroglyphidio, where Claparede noticed tliem as long ago as 18GS *, in the Oribatidte, 

 where I described them and called them the expulsory vesicles t, &C. They contain a 

 yellowish oily fluid, and have been generally admitted to be excretory organs ; they appear 

 to be sacs closed on the interior side, their only opening being extei-nal. 



Musculation. 



I do not find tbat the extremely pretty levatores ani muscles, and the neighbouring 

 muscles which serve to compress the hind part of the aljdomen dorso-ventrally, have been 

 figured or described. Pig. Ti (PI. XXXV.) is from a transverse section of JI. h'wsiitus 

 passing through the anus, and the musculation will be so readily understood from that 

 drawing that I do not think I need describe it. The drawing is made from a 

 preparation of a specimen killed with boiling water, and the anus is consequently 

 rather unnaturally protruded, but I selected it as showing the construction better 

 than other specimens where this had not occurred. 



Summary. 



For the convenience of those who wish to see at a glance whether this paper contains 

 anything likely to interest them I beg to summarize it as follows. 

 I suggest that it contains : — 



1. A series of observations on the coition of the Gamasina), showing a mode previously 

 quite unknown except from a partial description of a single case formerly recorded 

 by mc ; and only less curious than that of the spiders, but entirely different therefrom. 



2. Some considerable ditfereuces in the male sexual organs from any previously 



* " Studien an Acaridcn," Zeitschr. f. wiss. Zoul. xviii. Bd. pp. 44.5, 540, Taf. xxxv, 

 ■j- ' British Oribatidtv,' Ray Soc. p. 179. 



