inteejSal anatomy of buella. 



487 



oiihvard horn the central portion. The transverse muscles are inserted at both ends at 

 the level of the tioor of the pharynx; tlrus, when they contract, instead of pulling the 

 lateral edges of the roof of tlie pharynx together they straighten losing their arched 

 lorm, and then press upon the portion of the upper surface of the pharynx lyino> 

 immediately beloAV them respectively, and thereby effectually close it. I have not 

 liitherto detected similar curved constrictor pharyngis muscles in any of the Acarina. 



T/ie (EsoxjIukjuh follows immediately upon tlie pharynx, and is, as usual, a long and 

 substantial membranous lube m the median line of the body, runnin"- rio-ht through the 

 centre of the brain ; its com-se being backward and slightly upward. There is an 

 indication of its being a little plicated into shallow longitudinal folds to allow of 

 expansion and contraction ; it hardly .stains at all, but certain scattered, very minute 

 nuclei on its exterior surface stain deeply. The folding and certain projections on the 

 inner surface of the oesophagus produce a very irregular lumen (fig. 28) in the o<reater 

 part of the anterior portion of the organ ; although at one point the lumen is circular 

 and extremely minute. Something like this irregular lumen is figured, but not 

 described, by Nalepa in Tyroglyphns *. 



There is, however, one most important matter in which the oesophagus of Bdella is 

 utterly ditterent from the corresponding organ in all other Acarina the anatomy of 

 which is known to me ; this is that from the dorsal surface of the oesojjhao-us of Bdella 

 almost immediately behind the pliarynx, there springs an immense diverticulum 

 (tigs, 3, 4, 34), re) ; which, w^here it leaves the oesophagus, is a tube slightly smaller than 

 the oesophagus itself, and is surrounded by an annular constrictor muscle (^mo; fio-. 84) ; 

 it, however, almost immediately enlarges to a tube somewhat wider than the oesophao-us, 

 and thus continues for a short distance ; I call this portion the neck. At the distal end 

 of this neck the organ enlarges, either suddenly or gradually, and forms an immense 

 sac, either elliptical or pyriform ; botli the sac and the neck are capable of o-reat 

 expansion and contraction, and the size depends greatly upon the amount of their 

 contents for the moment ; they are usually considerably larger in the female than in the 

 male. Although, for these reasons, the size cannot be accurately stated, yet it may be 

 more or less gathered from the space which the organ occupies : the dorsal surface of 

 the sac adjoins the ventral surface of the azygous salivary gland ; its sides are embraced 

 by the pericibal salivary gland, which also curls over a portion of the dorsal surface 

 which is not covered by the azygous gland ; its posterior end presses against the anterior 

 end of the ventriculus, while its ventral surface overlies the oesophagus and the dorsal 

 surface of the supra-oesophageal ganglion of the brain. The organ is simply a mem- 

 branous sac with sloutish walls. There c;in, I think, be but little doubt of its function ; 

 it is, in my opinion, analogous to the so-called sucking-stomach in such Lepidoptera 

 as Danais archiiJpus-\, Sphinx lujmti-i, Foiitia b/rissicw t, and others, and in the Diptera 

 and some Hymenoptera, such us Cruhro. 



* "Die Auatomic dcr Tyroglyphen," !^itzb. k.-k. Akad. Wien, Bd. xc. Abth. 1 (18S4), p. 198, and Bd. xcii. 

 (1885), p. IIU, Taf. i. lig. 8. 



t E. Burgess, "Contributions to the Anatomy of the Milk-weed Butterfly (i>«n«i'4- arduppus),'" Auniv. Men:. 

 Boston Soc. lyat. Hist. 18bi). 



+ Newport, in Todd's ' C'yclopEedia,' article " Insecta,'' tigs. 43(J, 431. 



66* 



