4 Transactions of tlie Society. 



mounted for the IMicroscope, so that their appearance can easily be 

 verified by any one interested in the subject, although of course 

 difierent opinions may be entertained as to the correctness of the 

 conclusions which I draw from them. 



The dissections have chiefly been made under a Stephenson 

 binocular, with powers varying from an inch to ^ in. and low eye- 

 pieces ; they have, however, in cases requiring it, been verified 

 and examined under amplifications running up to over 1000 

 diameters. 



I think I may say that the tendency of my mind has been a 

 desire to confirm previous writers, and not to upset then- state- 

 ments. Where I am not able to agree with them, it is that I have 

 failed to obtain the same result, and that the actual organs before 

 me do not seem to me to agree with the accounts. 



The principal differences which I find in the internal organs 

 are in the respiratory system, and the reproductive system. I find 

 difi'erences of lesser importance in the alimentary canal ; and I 

 believe that I have traced some secreting organs not before re- 

 corded ; these are the points upon which 1 intend to touch ; and, 

 finally, I shall mention two matters in connection with the exo- 

 skeleton which seem to me to be worthy of notice. 



It is necessary to describe the alimentary canal in order that 

 the varieties, &c., which it displays may be understood, although 

 Nicolet figured the greater part of it correctly in one species. 



The Alimentary Canal. 



In the Oribatidm the alimentary canal is somewhat short and 

 simple, that is to say, there is a comparative absence of convolu- 

 tions in the hind-gut, and the very numerous caecal prolongations 

 of the mid-gut found in many allied groups, as the Aranea, 

 Ficnogonicla, &c.. are reduced to two, which, however, are usually 

 of great size and importance. The proportions of the parts of the 

 canal, and the size and arrangement of the ca;ca, vary greatly in 

 different species, but, as far as my experience goes, the divisions of 

 which it is composed are always the same. 1 say " as far as my 

 experience goes,'" because I have not dissected anything like the 

 whole of the species. 



The canal is composed of the oesophagus, the ventriculus, a 

 short small intestine, the colon, and the rectum, terminating in the 

 anus and anal plates ; of these the two first are almost horizontal, 

 and are placed in a straight median line near the dorsal surface ; 

 the small intestine turns downward and slightly forward, and the 

 colon and rectum are more or less perpendicular, and lie beneath 

 the ventriculus, or almost so ; the result of this is, that, when the 

 dorsal shield is removed, the oesophagus and the ventriculus, with its 



