$ 346. THE INSECTA. 441 
4 
These always consist of several very long small tubes which, either 
‘separately, or by means of one or two common excretory ducts, are inserted 
upon the posterior or pyloric extremity of the stomach. These ducts are 
sometimes dilated, bladder-like, at their point of insertion. The opposite 
extremity of these uriniferous canals either terminates caecally, or passes 
arcuately into that of another. When, as is usual, they are very long, 
they embrace the digestive canal with numerous irregular convolutions. 
With certain species, they creep, by their anterior extremity, between the 
tunics of the stomach, or by their posterior between those of the colon ; this 
remarkable relation has often led to the opinion that these organs have 
two outlets into the digestive canal. 
These vessels are yellowish or brownish in color, and often slightly vari- 
cose.“ They are composed of an external homogeneous tunic filled inter- 
nally with cells. These last are very large, and are disposed rather in 
rows, than adjacently ; and nowhere can there be perceived in the interior 
of the vessels a glandular canal defined by a special epithelium. ach cell 
contains a clear, colorless nucleus, and a multitude of very fine granules 
which appear black by direct light, but by reflected light present a dirty- 
yellow or brown, rarely a green or red, aspect. The granular contents 
of the cells, which give to these vessels their peculiar color, are scattered, 
when the cells are ruptured, through the intercellular spaces, and flow 
gradually into the digestive canal, Thus excreted, they accumulate ijn the 
colon or in its caecal appendage, and are evacuated with the faeces, or 
‘separately, as a troubled liquid of a color varying according to the 
species. © 
§ 346. 
The Malpighian vessels present numerous modifications as to their num- 
ber, their length, their points of insertion, and their modes of grouping, in 
the different orders of the Insecta.” 
With the Aptera, they are of median length; with the parasitic species, 
and with the Lepismidae, they are four in number; and six with the Pod- 
uridae.@ 
The Hemiptera have never more than four of these vessels, which are 
pretty long, whose extremities are looped with the Hydrocorisae and many 
3 L. Dufour has clearly demonstrated the usual 
caccal terminations of these vessels; see Ann. d. 
Sc. Nat. XIV. 1840, p. 231, Pl. XI. fig. 11 (larva 
ofa Mordella), and XIX. 1848, p. 155, Pl. VI. fig. 
9 (Hammaticherus heros). 
4 The uriniferous canals of Melolontha vulgaris 
and Sphinz ligustri form, in this respect, a re- 
maikable exception. In a great part of their 
‘course, they have on each side short caeca, pecti- 
nately disposed ; see Ramdohr, Abhandl. &c. Taf. 
VILL. fig. 1,2; LZ. Dufour, Ann, d. Sc. Nat. III. 
1823, Pl. XIV. fig. 4,55; Straus, Consid. &c. Pl. 
V. fig. 6,10 (Melolontha) ; and Newport, Cyclop. 
loc. cit. p. 974, fig. 432 (Sphinz). 
5 For the intimate structure of these vessels, see 
Hl. Meckel, in Miilder’s Arch. 1846, p. 41, Taf. II. 
6 With the holometabolic Insecta, the urine is 
eV ted isolately, especially when.they approach 
the completion of their pupa-state. It is well 
known that the Lepidoptera, when bursting from 
their pupae, emit a considerable quantity of urine, 
of a variable color. In the larva and pupa of 
Myrmeleon, it is gradually accumulated toa large 
quantity of a rose-color, in the digestive tube, and 
which the perfect insect immediately discharges on 
leaving the pupa-envelope, as a solid or elongate 
ovoid body. Réaumur (Mém. VI. 10 mém. Pl. 
XXXIV. fig. 12, 13) and Roesel (Insekteubelust. 
IIL. p. 123, Taf. XX. fig. 28, 29) have taken this 
urinary concretion for the egg of this insect. Some-~ 
times there is precipitated in the urine, red crystals 
of a quadra-pyramidal form; for example, with 
the larvae of Sphinzg and Ephemera. 
1 For these modifications in the different orders 
of Insecta, see the figures belonging to Ram- 
dohr’s work (Verdauungswerkz. &c.); those of 
Suckow, in Heusinger’s Zeitsch. III. and L. Du- 
Jour, Sur les vaisseux biliares ou le foie des In- 
sectes, in the Ann. d, Sc. Nat. XIX. 1843, p. 145, 
Pl. VIL~-IX. : 
2See Treviranus, Verm. Schrift. II. Taf. IIT. 
fig. 1 (Lepisma), Swammerdamm, Bib. der Nat 
Taf. IL. fig. 2 (Pediculus), and Nicolet, loc. cit. 
Pl. IV. fig. 2 (Podura). 
