258 THE WOODLANDS. 



emit from the spinners a small quantity of viscid 

 fluid, which is drawn out into fine lines by the as- 

 cending current occasioned by the rarefaction of the 

 air contiguous to the heated ground. Against these 

 lines the current of rarefied air impinges, till the 

 animals, feeling themselves acted upon with sufficient 

 force, quit their hold of the objects on which they 

 stand and mount aloft." 



Spiders do not always ascend into the atmosphere 

 by a vertical movement, but are observed to sail 

 through it in various directions ; and the fact admits 

 of an easy explanation when the disturbing causes by 

 which that subtle medium is liable to be affected are 

 taken into consideration. A direction parallel to the 

 horizon will be given by a current of air moving in 

 that plane ; a perpendicular one by the ascent of the 

 air rarefied; and directions intermediate between these 

 w r ill in general depend upon the composition of forces. 

 When the horizontal and vertical currents are equal 

 in force, the line of direction will describe an angle 

 of 45 Q nearly with the plane of the horizon ; but when 

 their forces are unequal, the angle formed with that 

 plane will be greater or less as one current or the other 

 predominates. 



The manner in which the lines are carried out from 

 the spinners by a current of air appears to be this. As 

 a preparatory measure, the spinning mammulae are 

 brought into close contact, and viscid matter is emitted 

 from the papillae ; they are. then separated by a lateral 

 motion, which extends the viscid matter into fine 

 filaments connecting the papillae ; on these filaments 

 the current impinges, drawing them out to a length 



