128 INTERNAL ANATOMY OF INSECTS. 



or infiltration, through the pores of the skin a ; a cir- 

 cumstance which seems to indicate a certain conforma- 

 tion of the pores both as to size and figure, so as to 

 enable them to admit only one peculiar product. 



In treating on this subject, I shall first consider the 

 organs of secretion, and next their products. 



I. Organs of Secretion. In general, these are mem- 

 branous vessels that float in the blood or nutritive fluid, 

 and secrete from it a peculiar substance. They may be 

 denominated according to their products Silk-secretors, 

 Saliva-secretors, Varnish-seer etor. Jelly or Gluten-secre- 

 tor, Poison-seer "etor, and Scent-secretors. 



i. Silk-Secretors (Sericteria). These organs are most 

 remarkable in the caterpillars of the nocturnal Lepido- 

 ptera or moths, especially in that tribe called Bombyces, 

 to which the silkworm belongs : but this faculty is not 

 confined to these insects, but is shared by many other 

 larvte in different Orders; and in one instance at least, by 

 the imago. In general, the outlet of the silk-secretors is 

 at the mouth / sometimes, however, as in the larva of 

 Myrmeleon and the imago of Hydropkilus, its exit is at 

 the anus. The first is the organ which in the silk-worm 

 provides for us that beautiful substance from which the 

 animal takes its name. There are always two of these 

 vessels, which are long floating tubes, growing slender 

 towards the head of the insect, where they unite to form 

 the spinneret (fusulus) before described b , which renders 

 the silk. Their lower extremity also is commonly more 

 slender than the middle, and is closed at the end. These 

 organs are usually very much convoluted and twisted c . 



a Cuv. Anat. Comp. iv. 103-. h VOL. III. p, 124. 



c Malpigh. DC Bombyc. t, v./. 2. Swamrn. t. xxxiv./. 5. Lyonet, 

 /. v./. 1. 



