THE INSECTA. 



423 



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

 contains fi'om 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 anil gizzard correspond to 

 parts of tlie same names with birds. The ileum, 

 which is usually regarded as analogiius to the small 

 intestine of the Vertebrata, probably plays a very 

 subordinate part in the act of digestion. Burmeis- 

 ter thinks that it serves only to conduct the chyme 

 or chyle, but with certain species where it is very 

 long, it is probably the seat of a second digestion. 

 Tlie caecum often serves to receive the secretory 

 product of the Malpighian vessels, and therefore 

 belongs rather to the urinary than to the Chylo- 

 poietic apparatus (see § 316). 



i It is hardly comprehensible how organs so com- 

 III )n with the Insecta, should, as yet, be so little 

 known. 



S uoamme.rdamm , however, observed them with 

 Apia melli/ica (Bib. der Nat. Taf. XVIII. fig. 1), 

 and Siickow {Heii,sin^er\i Zeitsch. III. p. 21, Taf. 

 VI. hg. 121, 12S) has mentiuncl them with Vespa 

 crauro, avid Apis vieUtJica, under the name of 

 callous swellings. Hrandt and Ratzehii.n!, Mediz. 

 Z.ol. II. Taf. XXV. tig. 2.) {Api.i mcUiJica), as 

 well as Biirmejster (Handb. &c. I. p. IIH) speak 

 of them very slightly. L. JJufour (Recherch. 

 siir les Orth opt. &c. p. 396, 427), lias figured them 

 with vari )U3 Orthoptera, Ni;uroptera and llymjn- 

 o|itera under the name of Boutons cliarniis ; 

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

 4 il, (Cara'xts ■mnn.iLis))haa designated them as 

 tiiaiidular protuberances. All the figures al)ove 

 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 

 Ramdo/ir, Abhandl. Cib. d. Verdauungswerkz. &o. 

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

 Taf. IX. fig. 153. The four with Melophas^as 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 Adela, have, by exception, only 

 six. Treviranus (Verm. Schrift. II. p. 106, Taf. 

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

 p. 184, PI. XVIII. fig. 6) have taken these organs 

 for glands with Papilio. 



■t The digestive canal is probably organized in a 

 similar manner with the larvae of the Hymen.iptera 

 and the Diptera, which are parasitic in the bodies 

 of other Insecta.* 



•5 For the digestive tube of the Insecta, beside the 

 works already cited of Swammerdamm, Gaede, 

 Burmeister, Lacnrdaire, and Newport, see. 

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

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

 X.X. p. 48 ; and Suckow, in Heusinser's Zeitsch. 

 III. p. 1. 



6 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 {Muller^s 

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

 larvae of wasps and hornets, concludes that a 

 ^traight alimentary canal opening at the posterior 

 Ktremity is always present, but that only the mus- 

 tiilar 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 larval 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. 



