The Internal Anatomy of Spiders 



(Fig. 143). They have been found in all species studied. In Aranea 

 there are about one hundred in each cluster or four hundred 

 in all; but in some spiders there are only a few of them. They 

 open through the first type of spinning tube, those with a long, 

 more or less curved base, and a slender straight tip (Fig. 172, a). 

 The name applied to these glands was suggested by the 

 botanical term acinus, which is applied to one of the kernels of a 

 fruit like a raspberry. A single gland resembles an acinus in 

 form; each of the four clusters of these glands resembles a berry. 

 The aciniform glands are nearly spherical and consist of an 

 epithelium invested by a peritoneal membrane (Fig. 173). The 

 epithelium is not continued into the duct. All parts of the 

 gland give the same reaction to stains. 



I have determined by direct observation that the swathing 

 band is formed of silk from these glands. This fact is easily 

 determined by feeding a spider confined 

 in a glass tube. 



Thepyriformor pear-shaped glands. — 

 There are two clusters of these glands, 

 one for each of the fore spinnerets 

 (Fig. 143). They have been found in 

 all species studied. In Aranea there are 

 Fig. '173. about one hundred in each cluster, or Fig. 174. 

 an two hundred in all, but some spiders A 



ACINIFORM . , , , ., T , PYRIFORM 



gland nave ornv a ' ew °' them. 1 hey open gland 

 through spinning tubes of the second 

 type (Fig. 172, b), in which the basal part is short, the tip 

 twice as long as the base and curved. 



These glands are elongate and consist of an epithelium in- 

 vested by a peritoneal membrane (Fig. 174). The epithelium is 

 not continued into the duct. The part of the gland next its mouth 

 gives a darker colour reaction to stains. Owing to this these 

 glands are easily distinguished in stained preparations. 



The function of the pyriform glands is the formation of the 

 attachment disks. The making of these disks by a spider con- 

 fined in a vial can be easily observed. 



The ampullate or bellied glands. — These are referred to by 

 certain writers as the cylindrical glands; but this name has been 

 applied to the type of glands described next. There are usually 

 four ampullate glands; but frequently there are six or eight, and 



172 



