42 AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



difference in size and form is perhaps largely due to the presence in 

 greater or less quantities of the liquid silk contained within the glands. 

 The caudate extensions of the pyriform part manifestly permit the secre- 

 tion and storage of larger quantities of spinning material. 



The Cylindrical glands, cy.g, have been considered by Meckel under two 



distinct forms, according as they have in one case an ampullate extension 



towards the duct, or in the other case are simply cylindrical 



Cylin- tubes. These forms he denominates Cylindrical and Ampullate. 



They appear, however, to be the same glands, exhibited under 



different conditions; and even according to Meckel they have the 



same structure and discharge from the same character of spinning spigots. 



They appear to be, as Bucholz and Landois regard them, but one gland. 



The difference in their form is probably due to the same cause by which 



the somewhat similar difference in the form of pyriform glands has been 



explained, namely, the presence of more or less of the secreted spinning 



substance. The number of cylindrical glands is eight, four of which are 



located on each side of the body. 1 



These glands represent very long cylindrical tubes, which extend from 

 the root of the spinnerets to the fore part of the body, near the breathing 

 organs. Thence, bending with waving convolutions, they return to their 

 origin. If they were stretched out entire, their length would almost equal 

 the length of the animal itself, of which, perhaps, they occupy only a third 

 part. This extraordinarily long gland terminates with a double fold be- 

 neath the lower end of the gland and the spinneret, which if stretched out 

 straight would exceed the length of the whole gland section. On the walls 

 of the gland is a simple stratum of gland cells, whose diameter is 0.020 

 to 0.024 mm. They are precisely like the cells of the pyriform glands, 

 and like them are filled with a great number of minute shining globules 

 of spinning substance. 



In the direction of the duct, the tubular part of the gland enlarges 

 greatly into an elliptical, ampullate extension, am, Fig. 35, from which the 

 duct proceeds. The construction of this ampullate swelling is 

 The Am ' the same as that of the cylindrical section, and in fact the swell- 

 Duct ' * n ma y De caused simply by the accumulation of spinning 

 material in the lower part of the gland, which thus rounds out 

 that part into an ampulla?, am. 



The duct of the cylindrical gland, c.du, has at its origin a width of 

 0.065 to 0.070 mm. (one three-hundred-and-fiftieth of an inch) and runs, 

 . quickly narrowing at first, to the root of the spinneret; thence 

 cal 'Suet ^ returns again, folded like a bent knee, k, and once more doub- 

 ling (do.) and proceeding downward discharges through its appro- 

 priate spinning spigot, a brown obtuse. cone on which stands a clear trans- 



1 Meckel and Oeffinger both report six glands of this kind on either side. 



