SILK SPINNING AND HANDIWORK 57 



The cribellar glands are found only in spiders that have a cribellum 

 a flat spinning plate and are used in conjunction with the calamis- 

 trum, a comb of hairs on the hind metatarsi. The comb-footed 

 spiders of the family Theridiidae possess all six of the remaining 

 types of glands, and are the only ones having lobed glands, which 

 secrete the material of the swathing film. These spiders thus are 

 provided with one more set of glands than their close relatives, the 

 sedentary orb weavers and the linyphiid spiders. 



Even the oversimplified classifications of Apstein and others 

 demonstrate conclusively that the spinning organs and glands of 

 spiders are the most complicated structures known for the produc- 

 tion and utilization of silk. The several types of glands and the 

 uses of their silk products are enumerated below: 



/. The aciniform, or berry-shaped glands. These glands are 

 found in all spiders and are characterized by their nearly spherical 

 shape and resemblance to various berry fruits, such as a raspberry. 

 Four clusters, each containing from a few to as many as a hundred 

 glands, send the silk through each of the posterior and median 

 spinnerets. The swathing band is a product of these glands. Ac- 

 cording to Apstein, they also produce the ground lines for the 

 viscid drops. 



2. The pyriform, or pear-shaped glands. Also found in all 

 spiders, these glands occur in two clusters of a few to one hundred 

 or more, and communicate with the front spinnerets. The making 

 of the attachment disks is one of their functions, but they some- 

 times contribute wild threads to the thicker draglines. 



3. The ampullate, or bellied glands. Known in all spiders, these 

 usually are present as four large, long, cylindrical glands, but fre- 

 quently there are six, eight, or even twelve. They open through 

 spigots which, when four glands are present, are located on the 

 inner side of each of the front and middle spinnerets. Most of the 

 dry silk of spiders, the dragline being the chief agent, is produced 

 in the ampullate glands. Comstock has suggested that the ground 

 line of elastic silk in the orb weavers is produced by these glands, 

 two of which have been modified for the production of this impor- 

 tant element. The fact that the yellow silk of Nephila is spun from 

 the anterior spinnerets partially confirms this opinion. 



4. The cylindrical glands. These long, cylinder-shaped glands 

 are often wanting in males, and are lacking in the Dysderidae and 

 the Salticidae. They number six or more, and open on the inside 



