OP DIGESTION. 353 



which opens into the oesophagus through a long narrow canal. Conse- 

 quently they suck their fluid aliment in the same manner. The setae, 

 which lie in the sheath of the labium, are thrust into the substance 

 which they suck, moving up and down like a pump during the opera- 

 tion, and thus the fluids ascend into the stomach by the alternating 

 distension and contraction of the sucking bladder. If we attentively 

 observe a gnat or fly thus occupied, the opposed motion of the setae may 

 be distinctly seen, and we also detect that the blood does not flow in a 

 continued stream, but at distinct intervals; so that when the gnat has 

 swallowed a drop a fresh drop follows it, but there is a momentary 

 cessation of the operation between. 



The flea and the Diptera pupipara do not possess this sucking 

 bladder, and their proboscis differs by not possessing the lower fleshy 

 sheath ; they hereby approximate to the Hemiptera, whose rostrum is 

 articulated, and they likewise have no sucking bladder. According 

 to Treviranus * the setae (see 70), of which their rostrum is formed, 

 are hollow, and vessels originate from their cavities which open into the 

 first stomach by means of narrow canals (see PI. XX. f. 3.) ; the oeso- 

 phagus itself opens into or beneath the tongue, seated between the setae, 

 whither also the ducts of the salivary glands pass. He therefore 

 assumes that the liquid ascends the hollow setae, as in capillary tubes, 

 and passes into the stomach through the vessels. I consider this opinion 

 doubtful, as it appears to me too mechanical, for hereby the oesophagus 

 would become superfluous, and particularly as the Hemiptera thus 

 imbibe their food throughout their whole lives. I should prefer con- 

 sidering the lateral distension, which is found at the commencement of 

 the stomach in many bugs, and the pyriform distension at the end of 

 the oesophagus, into which the second stomach returns, as the analogue 

 of the sucking bladder, and thus suppose in them a mechanism con- 

 formable to that found in the other orders. Ramdohr also, who has 

 figured the intestines of many bugs, never found tubes conducting 

 from the setae to the stomach. 



219. 



Their own variety conforms tolerably with the various modes of their 

 taking food. Thus naturally fluid aliment can only be imbibed, and 

 that which is of a firm consistency must be bitten off and masticated. 



Annalen der Wetterauschen Gesellsch. f. d. Ges. Nat. I. 2, p. 171. 



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