THE INTERNAL ANATOMY OF INSECTS 



103 



(PentatoniicUe) the fluid is excreted through two openings, one on each 

 side of the lower side of the body near the middle coxse ; in the bed- 

 bug (Cimcx), the stink-glands open in the dorsal wall of the first three 

 abdominal segments ; in Dytiscus, the glands open on the prothorax ; 

 and in certain Coleoptera they open near the caudal end of the bodv. 

 These are merely a few examples of the many glands of this type that 

 are known. 



The cephalic silk-glaiids. — In the Lepidoptera, Trichoptera, and 

 Hymenoptera, there is a pair of glands that secrete silk, and which 

 open through the lower lip. These glands are designated as the 

 cephalic silk-glands to distinguish them from the silk-glands of certain 

 Neuroptera and Coleoptera in which the silk is produced by modified 

 Malpighian vessels and is spun from the anus. 



The cephalic silk-glands are elongate and coiled ; they often 

 extend nearly the whole length of the body ; the two ducts unite and 

 the single terminal duct opens through the lower lip, and is not 

 connected with the mouth cavity. These glands are a pair of 



salivary glands which have 

 been transformed into silk 

 organs. According to Carriere 



Fig. 1 20. — The salivary glands 

 of the honeybee (After 

 Cheshire). 



Fig. 121. — Theman- 

 viibular gland of a 

 honeybee. 



and Burger ('97), who studied their development in the embryo 

 of a bee, they are developed from the rudiments of the spiracles 

 of the first thoracic segment. In the later development they move 



