^347. 



THE INSECTA. 



445 



There is another category of secretory organs which, with many females, 

 open at the base of the ovipositor, but as they are intimately connected 

 with the act of oviposition, they will be most properly described with the 

 genital organs/^^' 



A very large majority of the holometabolic Insecta have, in their larvae- 

 state, silk-organs, the secretion of which they use, some, to weave a cocoon 

 when about to pass into the pupa-state, or to close a hollow refuge they 

 have sought ; others to fasten together foreign bodies for the fabrication of 

 their retreat. These organs are, therefore, most developed at the period 

 when these insects approach their pupa-state ; but with the larvae of the 

 Psychidae, Tortricidae, and Lasiocampadae, they are already active during 

 the first epochs of life. The silk-secreting portion of this glandular apparatus 

 consists of two long, somewhat flexuous, thick-walled caeca, situated on the 

 sides of the body, and continuous, in front, into two small excretory ducts, 

 whose common orifice is on the under lip, and usually at the extremity of 

 a short tubular protuberance.*'^' With the larvae of Myrmeleon, the silk- 

 apparatus is very remarkable, for the rectum itself is changed into a large 

 sac and secretes this substance, which escapes through an articulated spin- 

 ueret projecting from the opening of the anus.*^'> 



With the Apidae, there is a very remarkable Wax-secreting apparatus. 

 This wax is elaborated by the Workers under the form of thin discs, which 

 are formed between the imbricated posterior legs, without there having 

 been discovered, as yet, in this region, the orifices of any special glands. 

 It must therefore be supposed that it is produced by an exudation from the 

 thin membranes which connect the different parts of the legs.''"' Moreover, 

 many other Insecta have secretory products which transude through the 

 pkin without the existence of any special glandular apparatus, and which 

 are hardened by the air like wax. These products are usually whitish, 

 pulverulent, filamentous, or flocculent substances, which catch upon the 

 surfaces of bodies. '"^' 



13 See § 350. 



14 See Roesel, Insektenbeluat. III. Class. I. Pap- 

 ilionum nocturnorura. Taf. IX. {Bombyx) ; Lyonet, 

 Traite, &c., p. 498, PL XIV. XV. {Cussus) ; 

 Suckou), Anat. u. physiol. Untersuch. p. 29, Taf. 

 VII. fig. 31 (Gastropacha) ; Pictet, Recherch. 

 pour seivir A Thist. d. Phryganides, PI. III. fig. 1 

 \Phryganea). The decrease of these organs dur- 

 ing the pupa-state has been very carefully detailed 

 by Herold, Entwickelungsgesch. d. Schmetterl., Taf. 

 III. and by Suckow, loc. cit. Taf. II. {Pontia, 

 Gastropacha). 



15 See Reaumur, Mem. &c. VI. PI. XXXII. fig. 

 7, 8 ; Ramdohr, Abhandl. &c. Taf. XVII. tig. 1. 



16 For the intimate structure of the wax-secret- 

 ing portions of the skin with the workers of bees, 

 see Treviranus, Zeitsch. f. Physiol. III. p. 62, 

 225 ; and Brandt and Ratzeburg, II. p. 179, Taf. 

 XXV. fig. 18. The production of wa.x with bees has 

 lately been the subject of much research among 

 French naturalists. Milne Edwards has ad- 

 vocated the opinion before rejected by him, that this 

 substance is secreted by special glands. But L. 

 Dufour, after carefully-made researches, failed to 

 discover them. See the various memoirs on this 

 question in the Compt. Rend. XVII. and in the 



Institut. 1843, also in Froriep's neue Not. 

 XXVIII. XXIX. 



It is, moreover, easy to be convinced of the ab- 

 sence of these glands witli the bee-workers ; but 

 if certain Andrenidae are examined, there will be 

 found, on each side of their posterior tibiae, a small 

 pyriforni follicle with an excretory duct, and which 

 secretes an oily substance. 



1'' These cutaneous secretions are observed with 

 various Coccidae and Aphididae, whose entire bodies 

 they cover with a powdery or woolly substance. 

 With the females o( Dortfiesia, not only the entire 

 body is covered with a suljstance which forms a * 

 solid white crust, but also the eggs after their depo- 

 sition are invested with a similar envelope and 

 thereby glued to the abdomen of the mother. With 

 many male Coccidae, this secretion forms, at the 

 posterior extremity of the abdomen, a bundle of 

 very diverging, long, white and perishable hairs. 

 With some C'icadidae (Lustra and Flata), the 

 thorax and abdomen are covered, in places, by a 

 kind of mould of a similar origin. The larvae of 

 many Tentliredinidae (for example, Tenthredo 

 ovata), as well as those of certain Coccinellidae 

 (Scymnus), exude a liquid which, upon di-ying, 

 forms white flocci.* 



* [ § 347, note 17.] See upon the subject of these 

 secretions Dujardin (Mem. sur I'etude micros- 



38 



copique de la cire, in the Ann. d. Sc. Nat. XII. 

 1S49, p. 250); his observations were mad.? upoa 



