THORACIC GLANDS IN LAEY^ OF TRICHOPTERA. 407 



On Segmentallj disposed Thoracic Glands in the Larvse of the 

 Trichoptera. By GtUstaye GtIlson, Professor of Zoology at 

 the University of Louvain. (Communicated by Prof. Gr. B. 

 Howes, Sec. Linn. Soc.) 



[Eead 5th March, 1896.] 



In the course of some researches on the silk-glands o£ the Tricho- 

 ptera, miy attention was attracted by a pointed prominence on 

 the ventral face o£ the first thoracic segment of the larva. 



This chitiuous prominence looks very much like the spinneret 

 of certain larval Lepidoptera, though it is usually a little longer 

 than that. In fact it was taken for the spinneret by Reaumur *, 

 who had not detected the very short spinning-tube on the 

 labium. Eecently Prof. Miall, in bis excellent book on Aquatic 

 Insects t, has recognized that the thoracic plug-like organ is 

 not the spinning-tube (the labial spinneret being known to him). 

 He does not attempt, however, to determine its use and true 

 significance, but declares it to be an organ the function of 

 which is as yet unknown. 



A careful dissection of the ventral organs in the fore part of 

 the body led me to the discovery of some very interesting glands, 

 one of which is in connection with the afore-mentioned pro- 

 thoracic prominence. 



In JPhryganea grandis each of the three thoracic segments 

 bears one of these glands. All three are composed of two 

 bundles of slightly moniliform tubules, lying, on each side, 

 between the outer tunic and the body-wall (fig. 1). 



The tubules of each bundle unite to form one main tube which 

 passes obliquely towards the median line, where it joins its 

 fellow of the opposite side to form a common duct. This, in 

 the prothorax, is rather long ; it enters the base of the cuticular 

 prominence, at the tip of which it opens through a very tiny 

 aperture. There is a small reservoir at the point of junction of 

 the tubes. 



The glands in the meso- and metathorax are almost identical 

 in structure with that of the prothorax, being only a little 

 smaller in size and having a smaJler number of tubules. Their 

 common duct is, however, extremely short and opens freely on the 



* Eeaumur, 'Memoires pour servir a I'Histoire des Insectes.' Paris, 1734. 

 t Miall, ' The Natural History of Aquatic Insects,' p. 251. London, 1895. 



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