130 INTERNAL ANATOMY OF INSECTS. 



atrox) they consist of two larger and two smaller ones, 

 at the base of which lie many still more minute a . The 

 four larger vessels are wide in the middle, branching at 

 top, and below terminating in a narrow canal leading to 

 the spinnerets b . Treviranus thinks the fluid contained 

 in the lower minute vessels different from that furnished 

 by the larger ones bift for what purpose it is employed 

 has not been ascertained. 



ii. Saliva-secretors (Sialisteria). These are organs, 

 rendering a fluid to the mouth or stomach, that are found 

 in many insects, especially those that take their food by 

 suction, as the Hemiptera, Lepidoptera, and Diptem, 

 though they are not confined to the perfect insect, being 

 also in some cases visible in the larva. Swammerdam 

 was one of the first that discovered them, and he suspects 

 that they may be salival vessels ; though he, as well as 

 Ramdohr, thinks they are the same with the silk vessels 

 of the caterpillar c ; an opinion which Herold has suffi- 

 ciently disproved, by showing that at one period of the 

 insect's life they co-exist" 1 , and Lyonet discovered a very 

 conspicuous pair in the caterpillar of the Cossus, co-ex- 

 istent with the silk-secretors e . But the physiologist who 

 has given the fullest account of these organs is Ramdohr: 

 I shall therefore extract chiefly from him what I have 

 further to communicate with respect to them. 



They are variously constructed blind vessels, that are 

 present in almost all insects that take their food by sue- 

 tion, but are mostly wanting in those that masticate it. 

 They have been found, however, in Cryptorhynchus La- 



a Treviran. Arachnid. 43. t. vr.f. 42. o. p. 9. < Ibid, a, y. 



c Swamm. ii. 21. a. t. xxxvi./. 1. abed. Ramdohr 58. 



d Schmet. t. Hi./. 1. c Lyonet. 112. /. v./. 1. P, Q, R> S. 



