568 



Till': AMERICAN NATURALIST [Vol. XLI 



canal. Each pair of tubes unites in the first abdominal segment 

 to form a connnon thoracic division. These connnon tubes, extend- 

 ing forwards with many convolutions in the thorax, turn ventrad 

 just behind the developing heafl and passing on each side of the 

 sub-oesophageal ganglion, end in short ducts. These ducts unite 

 in the labial region to form the press which occupies more than 

 half of the common duct. 



In young larvae just hatched, and for several days later, the 

 glands show no convolutions whatever. They lie as straight 

 tubes, two on each side of the alimentary canal and extend caudad 

 to the antepenultimate segment (PI. 1, fig. 1). jNIoreover the 

 structure is the same throughout their entire length, no regional 

 differences occurring. Their walls are thick and their lumina 

 very small. Later they become much convoluted, and their 

 lumina are greatly distended, till in the mature larvae at time of 

 emergence from the host, the abdominal division has practically 

 ceased to secrete, becoming simply a reservoir for the already 



The silk nlaiids may be divided into two general divisions; 1.. 

 Secretory. l>. ( \,M.lii("ting. 



The Secretory Division. — The secreting division nuiy be con- 

 venienllv divided into two portions, abdominal and tli/.racic 



Thr ah,lomim,( pnrtiun (•<.... |)riM- that part ot' tlic uland .'xt<M.d- 

 ing ca.idad hum the point of j,i.,ctinv of the ulan.lular tubes in 

 tiie first abdominal segment. 



In the freshly hatched and y(.unu' larvae this portion consists 

 of two pairs of straight glanduhir tubes, one pair situated on eaeh 

 side of the alimentary catuil iV\. IJi-. 1). On .>aeli side th(> tuhes 



