44 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



Tree on a 



py-g 



spn 



parent tube from which proceeds a thick thread. In its course it runs 

 between the delicate external net like walls (n.w), which originated as a 

 continuation of the ampulla, and terminate close at the base of the spin- 

 neret. The walls are without ordinary cell formations. There is no dif- 

 ference in construction between the cylindrical and ampullate part of this 

 gland. Of the Treeform, or as Meckel denominates them Aggregate glands, 

 tr.g, there are five on either side, of which four discharge at the anterior 

 spinneret, and one at the middle. The secreting part of these 

 gj an( j g cons i s t s of a large, white canal, widening into many sacs, 

 which form together a roundish cluster, c, c, c. The duct, tr.d, 

 runs quite close to the middle of the cluster, like the umbilical cord from 

 the placenta in mammals. In the beginning it is straight and smooth, but 

 farther on is accompanied on its superficial part by a number of small blind 



sacs (bs), with thin necks. 

 Towards the end, the duct 

 becomes smooth again, and 

 enters the spool destined for 

 it, which is somewhat larger 

 than that of the cylindrical 

 glands. Soon after its exit 

 from the gland the duct has 

 a diameter of 0.160 mm., 

 but greatly narrows toward 

 the spinneret to 0.04 mm. 

 The duct appears, through- 

 out its entire length, spiral- 



, . , . , ,, 



ty tWlSted, W T ltllOUt lOrmillg 



g\ich folds as are Seen ill the 

 . 



cylindrical glands. 



Meckel further describes what he calls the Tuberose or Bulbous glands 

 (glandulae tuberosse), of which he says there is one on either side. (Fig. 36, 

 bl.g.) According to this author they are small, and consist of a few branching 

 tubes with knotted enlargements at short intervals, which pass finally into a 

 duct that unites with the duct of the large cylindrical gland (Ventricose gland 

 of Meckel), which leads into the middle spinneret. Buchplz and Landois, 

 however, declare that they have never been able to detect this gland, and 

 doubt its existence. I have seen somewhat similar glands in Argiope cophi- 

 naria, but have simply regarded them as one of the various forms of the 

 pyriform glands. 



A valuable study of the internal spinning organs of spiders was made by 

 Mr. R. H. Meade, and reported to the British Association as early as 1844. 1 



1 On some Points in the Anatomy of the Araneida or True Spiders, especially on the Internal 

 .Structure of their Spinning Organs, by R. H. Meade, F. R. C. S. ; British Association Reports, 

 1858, page 157, sq. 



FIG. 36. Glands of Epeira diademata. (After Meckel.) cy.g, 

 Meckel's cylindrical glands ; am.g, ampullate glands ; bl.g, bulbous 

 glands; py.g, cluster of pyriform glands leading into the spin- 

 neret,spn. 



