^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 soucjht ; others to fasten toa;ether 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- 

 neret 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 difierent parts of the legs.'^''^ Moreover, 

 many other Insecta have secretory products which transude through the 

 skin 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 flocculeut substances, which catch upon the 

 surfaces of bodies. '"^^ 



13 See § 350. Institut. 1843, also in Froriep's neae Not. 



H See Roesel, Insektenbelust. HI. Class. I. Pap- XXVIII. XXIX. 



ilionumnocturnorum. Taf. IX. (Bom6(/a-) ; Z,(/o«et, It is, moreover, easy to be convinced oftheab- 



Traite, &c., p. 49S, PI. XIV. XV. (^Cossus) ; sence of these glands with the bee-workers; but 



iSuc/cow, Anat. u. physiol. Untersucii. p. 29, Taf. if certain Andrenidae are examined, there will be 



VII. fig. 31 (Gastropacha) ; Pictet, Kecherch. found, on each side of their posterior tibiae, a small 



pour servir ^ I'hist. d. Phryganides, PI. III. fig. 1 pyriform follicle with an excretory duct, and which 



{P/iri/ganea). The decrease of these organs dur- secretes an oily substance. 



ing the pupa-state has been very carefully detailed 17 These cutaneous secretions are observed with 



by Herold, Entwickelungsgesch. d. Sclimetterl., Taf. various Coccidae and Aphididae, whose entire bodies 



III. and by Suckow, loc. cit. Taf. II. (Pontia, they cover with a powdery or woolly substance. 



Gastropacha). With the females ot Dorthesia, not only the entire 



15 See Reaumur, Mem. &c. VI. PI. XXXII. fig. body is covered with a substance which forms a 

 7> 8 ; Ramdohr, Abhandl. &c. Taf. XVII. fig. 1. solid white crust, but also the eggs after their depo- 



16 For the intimate structure of the wax-secret- sition are invested with a similar envelope and 

 ing portions of the skin with the workers of bees, thereby glued to the abdomen of the mother. With 

 see Treviranus, Zeitsch. f. Physiol. III. p. 62, many male Coccidae, this secretion forms, at the 

 225 ; and Brandt and Ratzeburg, II. p. 179, Taf. posterior extremity of the abdomen, a bundle of 

 XXV. fig. 18. The production of wax with bees has very diverging, long, wliite and perishable hairs, 

 lately been the subject of much research among With some Cicadidae (Lustra and Plata), the 

 French naturalists. Milne Edwards has ad- thorax and abdomen are covered, in places, by a 

 vocated the opinion before rejected by him, that this kind of mould of a similar origin. The larvae of 

 substance is secreted by special glands. But L. many Tenthredinidae (for example, Tenthredo 

 Dufour, after carefully-made researches, failed to ovata), as well as those of certain Coccinellidae 

 discover them. See the various memoirs on this (Scymnus), exude a liquid which, upon drying, 

 question in the Compt. Rend. XVU. and in the forms white flocci.* 



*[§ 347, note 17.] See upon the subject of these copique de la cire, in the Ann. d. Sc. Nat. XIL 



secretions Dujardin (Mem. sur I'etude micros- 1849, p. 250); his observations were made upon 



38 



