^ 338. 



THE INSECTA. 



423 



With nearly all Insecta in their perfect state, this colon or large intestine 

 contains from four to six organs of a peculiar structure and doubtful 

 function. These consist of transparent protuberances, disposed in successive 

 pairs, or forming a transverse series. They are round, ovoid, or oblong, 

 their base being sometimes surrounded by a horny ring, and they are trav- 

 ersed by numerous tuft-like tracheae.*^' The Lepidoptera, especially, are 

 remarkable for their numerous organs of this kind.^^' It is singular that 

 they are wanting in all insects during their larval and pupa states. 



The Anus of Insecta, in all their states, is invariably situated on the last 

 segment of the body. With the quiescent and non-feeding pupae, both the 

 anus and the mouth are wanting, but with the larvae of only the Strepsip- 

 tera, the Apidae, and the Vespidae, are both ileum and colon wanting at 

 the same time.'*' 



The form and disposition of the different parts of the digestive canal 

 vary infinitely, according to the habits of life and the states of development 

 of the Insecta in which they are observed. On this account it is very 

 difficult to make any general statement of the various structural relations.*"' 

 But that condition may be taken as the fundamental type which belongs 

 to those perfect insects whose life is pretty long and which have masticatory 

 organs. Such, therefore, will receive our first consideration. 



With the Coleoptera/*" the oesophagus is nearly always terminated by a 



tions of the stomach and small intestines of the 

 Mammalia. The crop and gizzard correspond to 

 parts of the same names with birds. The ileum, 

 which is usually regarded as analogous to the small 

 intestine of the Vertebrata, probibly plays a very 

 Bubordinate part in the act of digestion. Burmeis- 

 ter thinks that it serves only tu conduct the chyme 

 or chyle, but with certain species where it is very 

 I0T1.1;, it is probably tlie seat of a second digestion. 

 The caecum often serves to receive the secretory 

 product of the Malpighian vessels, and therefore 

 belongs rather to the urinary than to the Chylo- 

 p jietic apparatus (see ^ 31S). 



'i It is hardly comprehensible how organs so com- 

 m >n with the Insecta, should, as yet, be so little 

 known. 



Sivimmprdamm, however, observed them with 

 A.iis mellifica (Bib. der Nat. Taf. XVIII. fig. 1), 

 and Siic/cow (^Heusinger's ZeitscU. III. p. 21, Taf. 

 VI. fig. 121, 12S) has mentioned them with Fespa 

 crabro, and Apis meKi/ica, umler the name of 

 callous swellings. Brandt and Rntzebur'^, Mediz. 

 Zool.- II. Taf. XXV. fig. 2J {Apis meUijica), as 

 well as B:trmeister (Handb. &c. I. p. l-l'J) speak 

 of them very slightly. L. Dufour (Recherch. 

 fin- les Orthopt. &c. p. 396, 427), liis figured them 

 with various Orthoptera, Neuroptera and Ilymen- 

 opt'.'ra under the name of Boutons charnus ; 

 fi lally, Newport (Cyclopaed. &c. II. p. 970, fig. 

 424, (Carahiis monilis)) has designated them as 

 tiUi'idiilar protuberances. All the figures above 

 cited give the external form of these organs but not 



their internal structure. They are especially ap- 

 parent and four in number with the Muscidae ; see 

 Ramdohr, Abhandl. iib. d. Verdauungswerkz. &c. 

 Taf. XIX. fig. 2, M. M. ; and. Sue/cow, loc. cit. 

 Taf. IX. fig. \53. The four with Melophas^us are 

 very singular and different from those of the other 

 pupiparous Diptera, in that their external surface 

 is covered with small solid scales ; see L. Dufour, 

 Ann. d. Sc. Nat. III. 1845, p. 71, PI. II. fig. IS- 

 IS. 



3 I have counted, with the Zygaenidae, thirty of 

 these swellings, and nearly a hundred with the 

 Papilionidae, Noctuidae and Geometridae. Hepio- 

 lus, Tinea, and Adeia, have, by exception, only 

 six. Treviranus (Vei-m. Schrift. II. p. 10i5, Taf. 

 XII. fig. 4), and Lyonet (M6m. du Mus. &c. XX. 

 p. 1S4, PI. XVIII. fig. 6) have taken these organs 

 for glands with Papilio. 



4 The digestive canal is probably organized in a 

 similar manner with the larvae of the Hymenoptera 

 and the Diptera, which are parasitic in the bodies 

 of other Insecta.* 



■■J Fur the digestive tube of the Insecta, beside the 

 works already cited of Swammerda?nm, Gaede, 

 Burmeinter, Lacordaire, and Newport, see, 

 especially, Ramdohr, Abhandl. iib. d. Verdauungs- 

 werkz. &c. ; Marcel de Serres, Ann. du Mus. 

 XX. p. 48 ; and Suckow, in Heusinsrer's Zoitsch. 

 III. p. 1. 



5 The digestive organs of the Coleoptera have 

 been especially studied by L. Dufour {Ann. d. Sc. 

 Nat. II. III. 1824, and I. 1834). See, moreover, 



• [ § 334, note 4.] See, for the intestinal canal of 

 the larvae of Hymenoptera, Ed. Grube {Mulier's 

 Arch. 1849, p. 50), who, from examinations of the 

 larvae 6f wasps and hornets, concludes that a 

 ;rraii;ht alimentary canal opening at the posterior 

 extremity is always present, but that only the mus- 

 Lidar tunic forms the continuous tube, — the lining 

 membrane of the stomach ending caecally, and the 



same membrane of the intestine commencing cae- 

 cally, and, finally, that the intestine serves, during 

 the larifal state, only to receive the secretion of the 

 Malpighian vessels which are urinary organs. But 

 it is doubtful if the contents of the stomach are ex- 

 pelled by mouth during the larval state. This closed 

 pyloric end of the stomach is opened during the 

 transition to the pupa state. — Ed. 



