Observations on the Oribatidm. By A. D. Michael. 5 



cseca, are usually the only parts of the canal seen. The canal is, of 

 course, firmly attached round the cavity of the mouth, and at the 

 anus, but in other parts it seems to float freely in the general 

 body-cavity, with only very shght attachments, if any. If the 

 oesophagus be cut away from round the mouth, and the rectum 

 from round the anus, a hair may easily be passed under the canal, 

 and its whole length be drawn out on the hair without further 

 injury. _ 



Taking Nothrus theleproctus as a convenient type : — 

 The oesophagus is a long, thin, almost straight, tract of the 

 canal, extending from the mouth to the ventriculus, and having its 

 lowest point at the former and its highest at the latter. It has thin 

 walls, capable, however, of considerable expansion and contraction. 

 The cavity of the mouth being larger in diameter than the lumen 

 of the oesophagus, the latter necessarily widens somewhat as it 

 approaches the former, and the widened portion might, not unfairly, 

 be termed the pharynx ; posterior to this the oesophagus continues 

 of almost even circumference for the greater part of its course 

 through the cephalothorax ; near its posterior extremity it widens, 

 in some species this enlargement is considerable, and then forms an 

 ingluvies or crop, the jabot of Nicolet ; this writer correctly gives the 

 ingluvies as very much developed in Damseus geniculatus, plate I. 

 fig. 3, c ; in Dammus davipes it is even more developed and is almost 

 as large as the ventriculus. I cannot say that I have ever seen it 

 so large in other genera, but it is no doubt quite distinguishable in 

 many others. Nicolet also, in the same drawing, depicts the 

 oesophagus as being constricted at short intervals by circular bands 

 of muscle, so that it presents a moniliform appearance. I have 

 not been able to detect this moniliform effect in any other species 

 which I have dissected, but the bands of muscle are usual. In the 

 ingluvies of Damseus geniculatus these circular bands of muscle 

 are beautifully seen after the preparation has been stained with 

 logwood, and indicate that it is an expansion of the oesophagus, not 

 a separate stomach. Nicolet further states that an air-bubble is 

 invariably found floating in this ingluvies ; my own observations do 

 not quite confirm this ; a large air-bubble is certainly to be seen 

 very frequently floating in the canal, but it appears to me that it 

 is not by any means invariably present, and that, when present, 

 it is more frequently in the ventriculus than in the ingluvies ; it is 

 doubtless due to the creature's living chiefly upon liquid materials 

 derived from vegetable substances, and absorbed by a sucking 

 process, which accounts for the presence of liquid in considerable 

 quantities in the fore- and mid-guts, and for those parts not being 

 quite filled with it. 



The oesophagus continues the whole length of the cephalothorax, 

 and passes a very short distance into the abdomen ; it is sharply 



