1909] Anatomy a }id Relationship of spiders 15 



the genus Latrodectus and it certainly will help to establish 

 relationships between forms which would otherwise remain sep- 

 arated in the system. 



While studying the muscular system and articulations in 

 Pholcus I was struck by the regularity of the rows of hair on the 

 legs. A comparison of many specimens showed that this is a 

 constant character. The leg has not the form of a perfect cylin- 

 der, but shows in a cross-section a circle with flattened sides, repre- 

 sented diagrammatically in Fig. 2. There are in all 8 rows of 

 hair; two rows on the episynaxial surface (esp and esr), one on 

 the middle pro (mp) and one on the middle retro line (mr), 

 and four rows on the four edges (ep, er, hp, hr). We find the 

 same arrangement on each segment of all legs beginning with the 

 femur; but the tarsus of the fourth leg in both sexes has a ninth 

 row of hair on the middle hypo line. The onychium of each tar- 

 sus is surrounded in all legs by 8 bristles, two of which are unpaired 

 and belong to the tarsus. The structure of these bristles may 

 best be understood from the drawing. (Fig. 4.) 



The hair forming the eight rows on the femur and tibia is of 

 uniform structure. It is represented in Fig. 5, in its entire length 

 and a part of it on a larger scale in Fig. 6. It is characterised 

 by the spiral row of small spines reaching a little beyond its 

 middle. Each hair is inclined towards the distal end of the liml) 

 at an angle of from 27-30 degrees. In a female of 2 mm. cepha- 

 lothorax length the hair on the femur marked in Fig. 2 , with the 

 letters esp and esr is about 0.8 mm. long, while that forming the 

 other four rows is only 0.57 mm. long. In the tibia all rows con- 

 sist of hair of the average length of i.o mm. There are no tric- 

 chobothria on the femur and tibia, but on the latter are some 

 six or seven extremely small hairs without any special structure, 

 measuring about 0.06 mm. The hair of the metatarsus is con- 

 siderably shorter than that of the tibia, but still of the same 

 structure in its proximal two thirds. The longest hair is at the 

 base of the metatarsus measuring in the above individual 0.4 mm. 

 Towards the distal end of the metatarsus the hair becomes grad- 

 ually shorter and changes structure. It measures now only about 

 0.28 mm. loses the spiral of small spines, while the two basal 

 spines — the only ones remaining — become considerably stronger. 

 (Fig. 7.) There are besides some six or seven scattered hairs 

 measuring about 0.12 mm., simple at the proximal end of the 

 segment and toothed at its distal end, w^here it looks as represented 



