44 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



Treeform 

 Glands. 



parent tube from wliieii 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 si^in- 

 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 pai't of these 

 glands consists of a large, white canal, widening into many sacs, 

 which fonn together a roundi.sh cluster, c, c, c. The duct, tr.d, 

 runs c^uite close to the middle of tlie cluster, like the umbilical cord from 

 the placenta in mannnals. In the beginning it is straight and smooth, Init 

 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- 

 ly twisted, without forming 

 such folds as are seen in the 

 cylindrical glands. 



Meckel further describes what he calls the Tuberose or Bulbous glands 

 (glanduliE tuberosje), 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. Bucholz 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 cojjhi- 

 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 s}>i(lers was made by 

 Mr. It. H. Meade, and reported to the British Association as early as 1844.' 



Fig. 36. Glands of Epeira diademata. (After MeckeJ.) cy.g, 

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

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

 neret, spn. 



' On some Points in the Anatomy of the Araneidaor 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. 



