KJ^'OWLEDGE OF THE HYDEACHXIDAE. 275 



tiires as developed in that sirjgular low-type arthropod Peripatiis 

 figured and described by Prof. H. N. Moseley. 



Dermal Glands. 



The dermal glandular system throughout tlie Ilydrachnidae 

 attains to a very considerable degree of development, though in 

 no species hitherto described does it appear to exhibit so marked 

 a degree of difterentiation as has here to be recorded of Limnesia 

 histrionica. By so early an investigator as C. L. Koch,* the 

 ainiular orifices of the separate gland systems upon the cuticu- 

 lar surface were distinctly recognised, though, as already stated, 

 misinterpreted as stigmatal apertures. Since Claparede's 

 demonstration of their true nature in the cases of A tax crassipes 

 and A . ypsUophorus a like structural composition has been identified 

 by Kramer and Haller to obtain in a variety of forms, though 

 in none of these is it shown that the glands opening at the 

 stigmata-like apertures exhibit anything beyond a simple follicular 

 structure, though they may unite in a common excretory duct 

 for a short distance before arriving at the surface of the in- 

 tegument. It is noteworthy, however, that Haller, so far 

 as the apertures themselves are concerned, has observed and-: 

 delineated a species of Hygrohates in which these are differentiated^', 

 upon as many as two or three distinct plans. In the majority of" 

 instances these apeitures are closed by membranous valves andj 

 have associated in their immediate vicinitv a singjle hair or seta.^ 

 while the subjacent glands take the form of simple pyriform 

 follicles. In a second less abundant series the apertures are 

 simply circular, closed apparently by a sphincter muscle and 

 without an attendant seta. Haller prefers to identify these 

 with the circular areas recorded by Claparede of Atax crassijjes 

 as being readily affected by osmic acid, and further hazai-ds the 

 opinion that they may represent a modified water-vascular 

 system, anomalous though such a structure would be in con- 

 nection with an arthropodous type. Thirdly, he has distinguished 

 the existence, though more rarely, of paired oval apertures upon 

 the dorsal region, which, like those of the second order, are un- 



* Ubersicht der Arachiideusy-stcins, 1842. 

 JouRN. Q. M. C, Series II. No. GO. 19 



