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THE AMERICAN NATURALIST [Vol. XLI 



and it is not till about three days after hatching that the furrow 

 and attached muscles become clearly differentiated. Being func- 

 tional for such a short time its complete development does not 

 take place till late in the larval life. It is not till shortly before 

 emerging from its host that the press becomes completely developed 

 as it is not necessary that it should be fitted for spinning during the 

 entire lifetime of the larvae but only for the very short time occupied 

 in the buihhng of its cocoon. 



In srructure the press differs from that described for Lepidop- 

 ttM'a in that the lateral pair of muscles is not present, and from 

 tliar of the Trichoptera in that each dorsal muscle is single and not 

 divided into two distinct bundles as figured by Gilson. 



Fuiiciions of the Press. — The functions of the press in the Lepi- 

 doptera liave been carefully worked out by Gilson and Blanc and 

 there is no doubt that the functions of this structure in the Hymen- 

 optera are similar. These functions may be summed up as fol- 

 lows— 



1. The press modifies and regulates the form and diameter of 

 the two threads. 



2. It regulates the layer of "gres" or "gum" whicli surrounds 

 these threads. 



3. By the relaxation of the musdes tlie chitinoiis walls on 

 accomit .a' their elasticity, contract and hold the thread innnovahle 



( Jilson attributes to the press another function, that of forcinu' the 

 thread to the exterior when by accidtMit or voluntarily the thread 

 is broken in the spinneret. This is deniecl by HIaiic who holds 

 that the contraction of the .muscles of the press, distending its 

 lumen to the fullest extent, together with the pressure upon the 

 contents of the gland due to the elasticity of its walls, and the general 

 muscular contractions of the body, serve to force the thread to the 

 exterior when l)roken in the spinneret or even in the conducting 

 tube. 



