The greater number of spiders have four pairs of eyes (Fig. 98), but there may be only one, two, or three pairs; and certain cave spiders are blind. The eyes appear like little gems set in the front of the cephalothorax. They are most prominent in the jumping spiders, which stalk their prey on plants, logs, fences, and the sides of buildings. [Illustration: _Fig. 99. Spinnerets of a spider._] [Illustration: _Fig. 100. A group of spinning tubes._] [Illustration: _Fig. 101. Viscid silk from an orb-web._] [Illustration: _Fig. 102. Spinnerets and cribellum of a curled-thread weaver._] The most characteristic feature of spiders is their spinning organs. The silk is secreted in glands within the abdomen, and while in the body it is a fluid. It passes out through the _spinnerets_, which are situated near the hind end of the abdomen. There are two or three pairs of spinnerets. These are more or less finger-like in form, and sometimes jointed (Fig. 99). Upon the end of each spinneret there are many small tubes, the _spinning tubes_ (Fig. 100), from which the silk is spun. Some spiders have as many as one hundred and fifty or two hundred of these spinning tubes on each spinneret. Ordinarily the tips of the spinnerets are brought close together, so that all of the minute threads that emerge from the numerous spinning tubes unite to form a single thread. Hence this tiny thread, which is so delicate that we can see it only when the light falls on it in a favorable way, is composed of hundreds of threads. It is not like a rope, composed of separate strands; for all the minute threads fuse together into a single thread. The change in the silk from a fluid to a solid cord, strong enough to support the weight of the spider, must take place quickly after the silk comes in contact with the air on leaving the spinning tubes; the minute size of the threads coming from the spinning tubes doubtless facilitates this change. Sometimes a spider will spread its spinnerets apart, and thus spin a broad ribbon-like band. We have seen a spider seize a large grasshopper which was entangled in its web, and rolling it over two or three times, completely envelop it in a sheet of silk spun from its spread-apart spinnerets. We have already described bands spun by orb weavers across the hub of the net in this way. It is supposed that the two kinds of silk spun by the orb weavers are spun from different spinnerets, and that the viscid silk comes from the front pair. When this silk is first spun, the viscid matter forms a continuous layer of liquid on the outside of it. But very soon this layer breaks up into bead-like masses--in a way similar to that in which the moisture on a clothes line on a foggy day collects into drops (Fig. 101).