

THE SILK OR SPINNING GLANDS 



Bordas, L. Appareil glandulaire des llyme'nopteres. (Ann. Sc. Nat. Zool.,xix, 



Paris, 1894, pp. 1-362, 11 Pis.) (See also p. 366.) 

 Berlese, Antonio. Le cocciniglie Italiane viventi sugli agruiri. Firenze, 1896, 



12 Pis. and 200 Figs. 

 With the writings of Mark, Minot, Locy, List, Krassilstschik, Nagel (1896), Miall. 



b. The silk or spinning glands, and the spinning apparatus 



The larvae of certain insects, chiefly those of the Lepidoptera, 

 possess a pair of silk or spinning glands (sericteries) which unite to 

 form a single duct opening in the upper lip at the end of the lingua, 

 which is modified to form the spinneret. (See pp. 71, 75.) All 

 caterpillars possess them, and they are best developed in the silk- 

 worms, which spin the most complete cocoon. Silk-glands also 

 occur in the larvae of the Tenthredinidae, in the case-worms or larval 

 Trichoptera, also in certain chrysomelid beetles (Donacia, Haemo- 

 nia), and in a weevil (Hypera). In a common caddis-worm (Lim- 

 nophilus) the glands are of a beautiful pale violet-blue tint, and two 

 and a half times as long as the larva itself ; viz. the body is 20 mm. 

 and the glands 55 mm. in length. 



In caterpillars the glands are of tubular shape, shining white, and 

 much like the ordinary simple tubular salivary glands of the imago. 

 When only slightly longer than the body they are twice folded, the 

 folds parallel and situated partly beneath and partly on the side of 

 the digestive canal ; not usually, when folded in their natural posi- 

 tion, extending much behind the end of the stomach; but in the 

 silkworms they are so long and folded as to envelop the hinder part 

 of the canal. In geometrid caterpillars the glands when stretched 

 out only reach slightly beyond the end of the body ; in Datana they 

 are half again as long as the body. Helm thus gives their relative 

 length in certain Eurasian caterpillars, and we add that of Telea 

 polyphemus : 



Vanessa io . . . . length of body 32 mm. ; of the silk glands 26 mm. 

 Smerinthus tilioe . . " " 63 " " " " 205 " 



Bombyx mori ..." " 56 " " " " 262 " 



Anthenea yamamaya, " " 100 " " " " 625 " 

 Telea polyphemus . " " 60 " " " " 450 " 



Thus in Telea the silk-glands are about 18.50 inches in length, 

 being about seven times as long as the body. 



For the most complete accounts of the spinning glands of Lepi- 

 doptera and their mechanism we are indebted to Helm and to Blanc, 

 and for that of the Trichoptera to Gilson. 



