974 



INSECTA. 



have seen in the recently detached vessel of 

 Vanessa urtictz ; and lastly of a third portion, 

 which consists of a minute vessel, extended 

 from the apparently ccecal extremity of the 

 middle portion of the organ, as formerly shewn 

 also by Lyonet in the Cossus. In the perfect 

 insect these parts still exist, but very much 

 reduced in size. In the Cossus Lyonet has 

 shewn four of these vessels, two of which, the 

 proper silk vessels, open by a single excretory 

 duct, and the others separately into the cavity 

 of the mouth. In some Coleoptera, as in the 

 Blapsida, these organs are formed of many 

 ramifying tubes united on each side of the 

 oesophagus into a single duct. In others, as in 

 the Orthoptera and Hymenoptera, they con- 

 sist of an immense number of rounded, opaque, 

 glandular bodies, aggregated together in small 

 clusters, which communicate by many small 

 ducts, inserted at irregular distances, with a 

 large and partially convoluted common or ex- 

 cretory duct, that opens on each side of the 

 mouth, so that each of these collections of 

 glands resembles a bunch of grapes or currants. 

 Each of these rounded granules, or acini if we 

 may so call them, receive a minute vessel, 

 but whether this is distributed over its surface 

 or is received directly into its substance we 

 .have been unable to ascertain. These aggre- 

 gations of salivary glands are usually situated 

 on each side beneath the oesophagus in the pro- 

 thorax, and are very distinct in the Orthoptera 

 and Hymenoptera, in which they have been 

 often noticed. Miiller has seen them in 

 Phasma, Treviranus in Apis, Burmeister in 

 Locust ida, Gryllida, and Termes, and we have 

 also seen them in Locust idte and GryllicUs among 

 the Orthoptera, and in Bombus, Apis, Antho- 

 plwra, and Athalia among the Hymenoptera. 

 Their existence in the latter genus is somewhat 

 interesting from the circumstance that the large 

 quantity of salivary fluid which these organs 

 seem calculated to produce appears to be 

 entirely employed in moistening the dry pollen 

 of flowers upon which the perfect insect chiefly 

 subsists, before it is passed into the oesophagus, 

 and not in the habits or in constructing of a 

 nest, as is the case with the bee, which always 

 employs it as a solvent for the wax in the con- 

 struction of its combs. In the latter insect, 

 according to Burmeister, the evacuating duct 

 of these organs is a minute spiral vessel re- 

 sembling a trachea, and empties itself into the 

 tube of the proboscis or ligula. The form and 

 number of these salivary organs varies in the 

 different classes; the usual number is two, 

 but in Apis Cimex and Pulex there are four, 

 each pair of which unite into one duct, while 

 in Nepa there are as many as six.* In the 

 Tabanidtf there are only two short ccecal tubes, 

 into which many minute vessels empty them- 

 selves .f Those gastric vessels, which are in- 

 serted at the commencement of the digestive 

 stomach we have above stated have been re- 

 garded as salivary organs, but there is consi- 

 derable doubt respecting their real function. 

 Burmeister considers them to be analogous to 

 the pancreas, but if this be admitted to be the 



case in the Orthoptera, those vessels also which 

 cover the exterior of the digestive stomach in 

 the carnivorous Coleoptera must be of the 

 same description, since both empty themselves 

 into the digestive stomach. But we cannot 

 coincide with him in this opinion, since frojn 

 an experiment which we shall presently notice 

 there is reason to believe that the fluid poured 

 into that cavity during digestion is of an acid 

 nature, analogous to that which is found under 

 similar circumstances in the stomach of ver- 

 tebrata; while that of the proper salivary 

 organs is believed to be alkaline, as was for- 

 merly supposed by llengger. Treviranus also 

 believed the same of the saliva of the honey- 

 bee, having witnessed its employment by this 

 insect in the formation of its combs. We have 

 also seen this insect reduce the perfectly trans- 

 parent thin white scale of newly secreted wax 

 to a pasty or soapy consistence, by kneading it 

 between its mandibles, and mixing it with a 

 fluid from its mouth, before applying it to 

 assist in the formation of part of a new cell, 

 so that we have good reason to believe that the 

 salivary fluid thus employed as a solvent for the 

 otherwise brittle wax is of an alkaline quality. 

 The Malpighian or supposed biliary vessels 

 (Jig- 432, p) usually enter the canal, as we 

 have seen, at the pylorus. They vary greatly 

 in number from two to twenty or even a hun- 

 dred, as in some of the Orthoptera and Hymen- 

 optera, but in all insects their function appears 

 to be similar. They are usually from four to 

 six in number, and are very long tubes that 

 pass from their insertion or opening into the 

 canal behind the pylorus directly forwards 

 about half way along the sides of the stomach, 

 and are then reflected backwards as far as the 

 ilium, around which and the colon they make 

 many convolutions, and in the Lepidoptera 

 terminate, or perhaps we ought rather to say 

 originate, each in a minute vessel, which be- 

 comes smaller and smaller in proportion to its 

 length, and in which we can perceive no dis- 

 position to form a ccecal termination, although 

 we have been unable to trace it to its origin, 

 which is certainly in the vicinity of the posterior 

 part of the colon. Of this we have satisfied 

 ourselves by following these vessels in the larva 

 of Odonestis potatoria, which the colour of 

 their contents, an opaque bright yellow, has 

 rendered practicable. We have traced them 

 until the yellow colour has disappeared in an 

 opaque white, and this has been also lost in a 

 perfectly transparent fluid, after which we have 

 been unable to follow the vessels further. In 

 other insects they appear to end in ccecal ex- 

 tremities, but we certainly could not observe 

 this in the larvae of Lepidoptera. It has also 

 been supposed by some anatomists that these 

 vessels form a double communication with the 

 alimentary canal, but this has entirely escaped 

 our observation. In the larva of Sphinx ligustri 

 and most other Lepidoptera these vessels are 

 covered by an immense number of minute oval 

 OEciform dilatations (Jig. 432, a), as is also 

 the case in some of the perfect Coleoptera, 

 Melolontha* as shown by Dufour, Straus 



Burmeister, op. cit, p. 146. 



t Id. 145. 



See Animal Kingdom, vol. i. fig. 38, c. 



