74 BRITISH rYROGLYPHID^!. 



few errors which his paper contains. In Gamasus, 

 however, the organs are large, conspicuous, and abun- 

 dantly functional ; discharging quantities of the white, 

 opaque, excrementary (? urinary) matter so well known 

 in the Acari. In the Tyroglyphida3 they appear to be 

 far smaller, more delicate, less evidently functional, 

 and altogether strike the observer as more rudimen- 

 tary, or, perhaps, nascent would be a more appropriate 

 word. 



THE Histology AND Physiology OF THE ALIMENTARY 



CANAL. 



The outer wall of the canal, as correctly stated by 

 Nalepa, consists of a structureless or almost structure- 

 less tunica propria, which looks like a fine line in sec- 

 tion. Nalepa says that the wall of the ossophagus 

 alone has a firm tunica propria projecting in three or 

 four folds into the lumen.* I have not noticed this to 

 any but a very slight extent in my sections of Tyro- 

 glyphida?, but in Bdella I have found the lumen of the 

 oesophagus between the pharynx and the brain almost 

 filled up by projections inward from the wall.f These, 

 however, appeared to me rather of an epithelial nature 

 than plications of the tunica propria ; but in Bdella, 

 with its oesophagus of small diameter and its solely fluid 

 nourishment, the necessity for great expansion does not 

 arise ; nor would the minute passage through the brain 

 allow of it. Nalepa, however, says that there is not 

 any. epithelial lining to the oesophagus in Ti/roglyphus 

 longior, and he says in general terms that the canal of 

 Garpoglyphus anonymus resembles that of T. loiicjior. I 

 have not observed any in the Tyroglyphidas. Ley dig did 

 not find any in Ixodes;\ Henkin does not mention any in 

 Trombidium, but he deals rather shortly with the his- 



* ' Abtheil,' i, p. 202, pi. i, fig. 8. 



f " The Internal Anatomy of Bdella," in ' Tr. Linn. Soc. London,' 

 vol. vi, pt. 7, p. 487, pi. xlii, fig. 28. 



J " Lehrb. d. Histologie," Frankfurt-a.-M., 1875, p. 230, 299. 



