$ 338. 



THE INSECTA. 



421 



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

 contains from four to sis 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 thi§ 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. 



VYith 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, probably plays a very 

 subordinate part in the act of digestion. Bunneis- 

 ter thinks that it serves only to conduct tlie chyme 

 or chyle, but with certain species where it is very 

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

 The caecum often serves to receive the secretory 

 product of the Malpighian vessels, and therefore 

 belongs rather to the m-inary than to the Chylo- 

 poietic apparatus (see § 346). 



2 It is hardly comprehensiljle how organs so com- 

 mon with the Insecta, should, as yet, be so little 

 known. 



Swammerdamm, however, observed them with 

 Apis mellifica (Bib. der Nat. Taf. XVIII. üg. 1), 

 and Suckoiv {Heusin^er''s Zeitsch. III. p. 21, Taf. 

 VI. fig. 121, 128) has mentioned them with Vespa 

 crabro, and Apis melUfica, under the name of 

 callous swellings. Brandt and Ratzebur^, Mediz. 

 Zool. II. Taf. XXV. fig. 29 (Apis mellifica), as 

 well as Burmeister (Handb. &c. I. p. 149) speak 

 of them very slightly. L. Dufour (Recherch. 

 sur les Orthopt. &c. p. 396, 427), has figured them 

 with various Orthoptera, Neuroptera aftd Hymen- 

 ojitera under the name of Boutons charnus ; 

 finally, Newport (Cyclopaed. &c. II. p. 970, fig. 

 424, (Carahas monilis)) has designated them as 

 Glandular 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 num))er witli the Sluscidae ; see 

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

 Taf. XIX. fig. 2, M. M. ; and Suckow, loc. cit. 

 Taf. IX. fig. 153. The fom- with Melophagus are 

 very singular and different from those of the other 

 pupiparous Diptera, in that then' external surface 

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

 Ann. d. Sc. Nat. III. 1845, p. 71, PI. U. 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 Lyonet (J16m. du Mus. &c. XX. 

 p. 184, 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.* . 



5 For the digestive tube of the Insecta, beside the 

 works already cited of Swammerdamm, Gaede, 

 Burmeister, Lacordaire, and Newport, see, 

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

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

 XX. p. 48 i and Suckow, in Heusinger''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 (Miiller^s 

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

 larvae of wasps and hornets, concludes that a 

 straight alimentary canal opening at the posterior 

 extremity is always present, but that only the mus- 

 cular tunic forms the continuous tube, — the fining 

 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 dui-ing the larval state. This closed 

 pyloric end of tlie stomach is opened dui'iug the 

 transition to the pupa state. — Ed. 



