194 '^^E SPIDERS OF EPPING FOREST. 



three in number, and in some species a number of minute supernumerary 

 claws are found, opposed to the ordinarj' ones. The eyes are sometimes 

 heterogeneous and sometimes homogeneous, in that case being of the diurnal 

 type. In some species the caput of the male is elevated in a most remarkable 

 manner, several of the eyes being often placed upon the raised portion. The 

 development of the tarsus of the male palpus from the simplest forms to the 

 most complex is very curious and interesting. Instead of the joint being 

 modified by a hollowing process to receive the palpal organs, it is split longi- 

 tudinally, this structure being very clearly seen in Pachygnatha, the genus 

 from which apparently the argiopiforra spiders have developed. In this 

 case we find both branches of the split joint very distinct and between them 

 the bulb of a very simple form and provided with but few appendages. From 

 this genus we can trace four distinct lines of development. The first series, 

 developing through Tetragnatha and Meta, gives rise to orb-spinning spiders 

 such as those of the genus Aranea and, possibly, the cribellate family 

 Uloboridae. The second terminates in the spiders of the " Walckenaera " 

 type, the males ot which possess, as a rule, curious cephalic prominences and 

 tibial apophyses upon the palpi. The third tends towards the higher types 

 of the " Linyphia " group with well developed spines upon the legs and highly 

 complex palpal organs. From the fourth we may trace the Theridiids, with 

 the aberrant family Pholcidae. With the structural development of these 

 various types the palpus has undergone great modifications, notably in the 

 gradual elimination of the external branch of the tarsus. The remaining 

 branch [i.e. the internal one) often becomes of a cup-shaped form, reminding 

 one strongly of the palpal tarsus of some of the Drassiform spiders, but with 

 the most important difference that the palpal organs are placed upon the 

 external surface of the joint instead of upon its under side. The palpal 

 organs, too, are usually far less enclosed by the tarsus than in the Drassi- 

 formae, the joint being often reduced to very small portions. The modified 

 external branch of the divided tarsus is found in several groups of Argiopi- 

 form spiders. It is rather conspicuous in many of the representatives of the 

 sub-family Linyphiinae of the family Linyphiidae and has been often referred 

 to under the term " falciform process.'' 



The Argiopiformae are for the most part deprived of tibial apophyses, 

 but in some groups, notably the sub-family Erigoninae these structures are very 

 strikingly developed. They are, however, of a form very different from that 

 exhibited by the Drassiformae. In the first place they are not nearly as 

 distinctly defined, being, as a rule more or less of the nature of expansions of 

 the joint itself, thus rendering it in many cases a matter of some difficulty to 

 decide exactly where the joint terminates and the apophysis commences. 

 Their position, also, is very characteristic, for they are usually placed upon 

 the superior anterior portion of the tibia, projecting considerably over the 

 tarsus and thus precluding any great vertical motion of the joint. The 

 lateral motion, necessitated by the external placing of the organs, is thus in 

 no way impeded. The genital aperture of the female, except in a few primi- 

 tive types, is furnished with epigynal plates, and often with a clavus also. 



The Argiopiformae almost invariably fabricate some form of snare. In 

 the majority of cases it consists of a horizontal sheet of irregular threads 



