^ 346. THE INSECTA, 441 



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 tilled 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. Each 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 in 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- 

 Tiridae.*^' 



The Hemiptei-a 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 Mi/rmeleon, it is gradually accumulated to a large 

 caecal terminations of these vessels ; see Ann. d. quantity of a rose-color, in the digestive tube, and 

 So. Nat. XIV. 1840, p. 231, PI. XI. fig. 11 (larva which the perfect insect immediately discharges on 

 of a Mordella), and XIX. 1S43, p. 155, PI. VI. fig. leaving the pupa-envelope, as a solid or elongate 

 9 (Hammatickerus heros). ovoid body. Reaumur (Mem. VI. 10 mem. PI. 



4 The uriniferous canals of Melolontha vulgaris XXXIV. fig. 12, 13) and Roesel (Ins.ktenbelust. 

 and Sphinx ligustri form, in this respect, a re- III. p. 123, Taf. XX. fig. 2S, 29) have taken thii 

 markable exception. In a great part of their urinary concretion fur the egg of this insect. Some- 

 course, they have on each side short caeca, pecti- times there is precipitated in the urine, red crystals 

 nately disposed ; see Ramdohr, Abhandl. &c. Taf. of a quadra-pyramidal form ; for example, with 

 VIII. fig. 1, 2 ; L. Dufour, Ann. d. Sc. Nat. III. the larvae of Sphinx and Ephemera. 



1823, PI. XIV. fig. 4, 5 ; Straus, Consid. &c. PI. 1 For these modifications in the different orders 



y. Qg. 6,10 (Melolontha); and Newport, Cyclop, of Insecta, see the figures belonging to Ram- 



loc. cit. p. 974, fig. 432 (Sphinx). dohr's work (Verdauungswerkz. kc.) ; those of 



5 For the intimate structure of these vessels, see Suckow, in Heu.iinger''s Zeitsch. III. and L. Du- 

 ll. Meckel, in Mailer's Arch. 1846, p. 41, Taf. U. Jour, Sur les vaisseux biliares ou le foie des In- 



6 With the holometabolic Insecta, the urine is sectes, in the Ann. d. Sc. Nat. XIX. 1843, p. 145, 

 evacuated isolately, especially when they approach PI. VII.-IX. 



the completion of their pupa-state. It is well 2 See Treviranus, Verm. Schrift. II. Taf in. 



known that the Lepidoptera, when bursting from fig. 1 (Lepisma), Swammerdamm, Bib. der Nat. 



their pupae, emit a considerable quantity of urine, Taf. II. fig. 2 (Pediculus), and Nicolet, loc. ciU 



of a variable color. In the larva and pupa of PI. IV. fig. 2 (Podura). 



