Observations on the Oribatidse. By A. B. Michael. 7 



numerous instances which I have examined, to the best of my 

 ability, I have not ever been able to detect food in the caeca, either 

 in specimens dissected out or in those observed in life where the 

 transparency of the chitin enabled me to do so, which was frequently 

 the case ; whereas it is rare to find the ventriculus or colon without 

 food contents. In addition to this, the structure of the walls of the 

 caeca, particularly near their distal ends, is different from that of 

 the ventriculus, they being thicker and much more glandular, and 

 the lumen smaller in proportion, often very narrow. These con- 

 siderations lead me to infer that their function is secretory, and not 

 simply that of an extension of the stomach, nor would there be any- 

 thing extraordinary in this being so, as a very similar arrangement 

 seems to exist in Apus, Limnadia, &c., the ends of the csecal 

 diverticula of the mid-gut being differentiated to form glandular 

 organs, and the same arrangement, carried to a greater extent, 

 prevails among the Malacostraca, &c. If these two large diverti- 

 cula have, as I suppose, the office of secreting fluids necessary for 

 digestion, it would explain to a great extent the apparent absence 

 of the so-called hepatic tubes, an absence observed by Nicolet, who 

 remarks that he was not able to detect any liver. In connection 

 with this subject, however, must be taken the observations which 

 will be found below as to the presence of diffused follicles, supposed 

 by some writers to have a hepatic function, over the surface of the 

 canal. 



The small intestine (plate I. figs. 1, 2, 3, 4, e). This portion, 

 forming the commencement of the hind-gut, may possibly be 

 considered as simply a portion of the colon, from which it is not 

 divided by any valve ; but as, although short, it is always present, 

 it may be convenient to treat of it under a separate heading. 



The entrance to the small intestine from the ventriculus is 

 always closed by a very efficient valve, which may occasionally be 

 seen to open in order to give passage to the balls of digested or 

 partially digested food. The small intestine proceeds from the 

 ventriculus at a point lying to the left of the median line and near 

 the pyloric end, but not actually at the end ; the entrance is situated 

 either at the edge of, or slightly on the under surface of the stomach, 

 but its position varies a little in different species. 



The colon (plate I. figs. 1, 2, 3,/), in all species in which I 

 have examined it, is an elliptical enlargement of the hind-gut, very 

 considerably smaller than the ventriculus, and usually clearly 

 defined, particularly at the posterior extremity, where it is provided 

 with a constriction or valve which usually completely closes the 

 entrance to the rectum ; it ordinarily turns downward, or slightly 

 forward, so as to be brought more or less under the ventriculus. 

 In a dorsal view when the notogastral shield has been removed 

 without disturbing the position of the canal, only the anterior end 



