The External Anatomy of Spiders 



It is also termed by some writers the ocular quadrangle or the 

 ocular quad. In descriptions of the jumping spiders (Attidae), 

 the term ocular quadrangle refers to the space occupied by all 

 of the eyes; and in this book this term is used only in this sense. 

 In the Lycosidae the four posterior eyes outline a trapeziform 

 area, which is described as the quadrangle of the posterior eyes. 

 The ocular tubercle. — In many spiders the eyes are situated 

 on an elevated portion of the head; this portion is termed the 

 ocular tubercle. 



The clypeus (clyp'e-us). — The space between the eyes and 

 the first pair of appendages, the chelicerae, is termed the clypeus. 



Frequently, in 



the tables, reference 



is made to the width 



of the clypeus. 



This is the distance 



from the front edge 



of the clypeus to 



the eyes nearest 



that edge. 



The face. — 



That part of the 



head which can be 



seen when the 



spider is observed 

 from directly in front is termed the face (Fig. 77). This term 

 is used in descriptions of certain spiders belonging to the second 

 suborder. It includes the clypeus and a part or the whole of 

 the eye-space. 



The front. — The anterior portion of that part of the head 

 lying immediately back of the clypeus is termed the front; the 

 front includes the eye-space, but has no definite limit behind. 

 The Chelicerae (che-lic'e-rae). — The first pair of append- 

 ages of the head are the cbelicercc. They are situated in front 

 of and above the mouth, from which they are separated by the 

 rostrum, and consist each of two segments, a large basal one, 

 and a terminal, claw-like one (Fig. 78). These are the appendages 

 with which the spider seizes and kills its prey. Near the tip of the 

 claw there is the opening of a poison gland (Fig. 79). 



The chelicerae are modified antennae; the)' are homologous 



Fir. 7. 



FACE AND CHELICER/E 



OF THERIDION 



Fig. 78. 



FACE AND CHELICER.E 



OF ARANEA 



99 



