INTERNAL 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 length of the caeca. 



Excretory Organs. 



In addition to the great Malphigian vessels there exist in some Gamasids, 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 Mcemo- 

 gamasus horridus 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 Avell known in other Acarina, e.g. in 

 the Tyroglyphidre, where Claparede noticed them as long ago as 1868 *, in the Oribatidse, 

 where I described them and called them the expulsory vesicles f, &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 external. 



Musculation. 



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

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

 figured or described. Fig. 74 (PI. XXXV.) is from a transverse section of H. hirsutus 

 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 Garnasinre, showing a mode previously 

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

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



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



* " Studien an Acariden," Zeitschr. f. wiss. Zool. xviii. Bd. pp. 445, 54G, Taf. xxxv. 

 f ' British Oribatidav Ray Soc. p. 179. 



