$ 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, 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. 
The 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 § 346). 
2 It is hardly comprehensible 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. fig. 1), 
and Suckow (Heusinger’s Zeitsch. III. p. 21, Taf. 
VI. fig. 121, 128) has mentioned them with Vespa 
erabro, and Apis meilifica, under the name of 
callous swellings. Brandt and Ratzeburg, Mediz. 
Zool. II. Taf. XXV. fig. 23 (Apis mellifica), as 
well as Burmeister (Handb. &c. I. p. 149) speak 
of them very slightly. 2. Dufour (Recherch. 
sur les Orthopt. &c. p. 396, 427), has figured them 
with various Orthoptera, Neuroptera and Hymen- 
optera under the name of Boutons charnus ; 
finally, Newport (Cyclopaed..&c. IL. p. 970, fig. 
424, (Carabus monilis)) has designated them as 
Glandular’ protuberances. All the figures above 
cited give the external form of these organs but not 
* [§ 334, note 4.) See, for the intestingl 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 
straight alimentary canal opening at the posterior 
extremity is always present, but that only the mus- 
cular tunic forms the continuous tube, — the lining 
membrane of the stomach ending caecally, and the 
their internal structure. They are especially ap- 
parent and four in number with the Muscidae ; see 
Ramdohr, Abhandl. ib. d. Verdauungswerkz. &c. 
Taf. XIX. fig. 2, M. M.; and. SuckowF loc. cit. 
Taf. IX. fig. 153. The four with Melophagus 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, Pl. IL. fig. 13- 
15. 
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. IL. p. 106, Taf. 
XIL. fig. 4), and Lyonet (Mém. du Mus. &. XX. 
p. 184, Pl. XVIIT. 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. iib. d. Verdauungs- 
werkz. &c.; Marcel de Serres, Ann. du Mus. 
XX. p. 48; and Suckow, in Heusinger’s Zeitsch. 
TIL. p. 1. 
6 The digestive organs of the Coleoptera have 
been especially studied by L. Dufour (Ann. 4. Sc. 
Nat. IL. ILL. 1824, and I. 1834), See, moreover, 
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. — Ep. 
