THE SPINNING ORGANS. 



41 



in diameter (about one-twelftli of an inch), h'ing close to the bases of the 

 spinnerets. (Fig 30, pj'.g.) In form the individual glands are long, oval, 

 pear shaped vessels, 0.22 mm. long, or, expressed approximately in linear 

 measure, say one hundi-ed and fifteen of average length would make an 

 inch. In Argiope I find the average length about one eighty-fifth of an 

 inch. At the inferior end they diminish grad- 

 ually, passing into a duct which narrows toM'ards 

 the point of discharge, and which, together with 

 a compact bundle of similar ducts, enters the 

 interior of the spinneret, each one to discharge 

 through its appropriate separate spinning tube. 

 The wall of the gland contains a single cell stra- 

 tum of a diameter of from 0.020 mm. to 0.024 

 mm. These cells contain a quantity of small 

 drops, which consist of a strong refractory sub- 

 stance that agrees in appearance with the spin- 

 ning material within the ducts. This glandular 

 wall incloses a large middle cavity, which is entirely filled with a viscous 

 liquid spinning substance. The duct which projects from this 

 Pyriform gj.^^j possesses at the beginning a diameter of 0.024 mm. ; nar- 

 ^° ^" rows very soon after exit from the gland to the diameter of 

 0.01 to 0.012 mm. That is to say, the termination of the duct is about 



one twenty-five-hundredth of 



PjTiform silk glands. 



an inch in diameter. At this 

 width it runs unaltered to its 

 place of exit from the spin- 

 ning tube. 



These pjTiform glands, as 

 preserved in Argiope cophina- 



ria, while agreeing in 

 Argiope's ,^^ f^^.^^^ ^ 



Glands. ^ . , , . , , ., 

 good deal m details, 



as shown by comparing the 



figures, 31, 32, and 33. Some 



of them are vermiform in 



shape. Fig. 33, v; some are 



strictly pyriform, p ; some are 



cordate, Fig. 32, c; and some 



have long caudal parts, Fig. 



31, pe, which in general appearance resemble the cylindrical glands, but 



are on a much smaller scale. The vermiform glands contain a yellowish 



white substance. The other glands contain a somewhat similar material, 



but of a deeper yellowish color, and broken into distinct globules; while 



others contain a brownish liquid which has already been alluded to. This 



Fig. 34. View of the cylindrical glands, cy.g, and treeform 

 glands, tr.g, of Epeira diademata. py.g, cluster of pyriform 

 glands, d, bundle of ducts leading therefrom, spn, a spin- 

 neret into which the glands lead. (After Meckel.) 



