174 Gyiiandry in Arachnida 



ceptible. Looked at from the front the cephalothorax seems a little distorted, 

 because the front row of eyes is more strongly curved on the left than on the right, 

 and the lateral slope of the caput is steeper. 



The mandibles are about equal in length (330 /i), but the right is rather broader 

 (190;i) than the left (170/i), and the setae are somewhat differently distributed. The 

 fore margin of the fang-groove bears on the right mandible 4, and on the left 5 teeth: 

 the former are slightly larger and unequally spaced ; the latter are equidistant, the 

 first and last being obviously smaller than the three between them. The sternum 

 is asymmetrical ; the left maxilla, seen from below, appears shorter than the right. 

 The left palp is a completely normal and fully developed male palp ; the right is 

 female without trace of abnormality. 



It is remarkable that in spite of the marked inequality of the two body-halves 

 the corresponding legs have joint for joint exactly the same length : but there is an 

 obvious difference between the metatarsi, and more particularly between the tarsi 

 of the first pair. The latter differ both in shape and pubescence : the left is slightly 

 clavate, at the base 55 /i, near the apex 70 /x wide ; while the right is of uniform 

 thickness (55 /x) except for the very apex ; the pubescence of the male (left) tarsus is 

 much denser and finer than that of the female right.... 



The asymmetry of the abdomen (1270/x long, 880 /x broad) is pretty obvious, the 

 right half being broader and more strongly curved than the left : a line from the pedicle 

 bisecting the fore part of the abdomen leaves all the spinners on its left side. The 

 right inferior spinner is 138 /x long, the left 130 /x, the former 95 /i, the latter BO^x wide 

 at the base. 



Very striking is the asymmetry of the genital area. The right half is more 

 strongly chitinized, the hind margin from the middle to the right dark, to the left 

 light ; the fissure on the left in which lies the entrance to the spermatheca, is abnor- 

 mally bent inwards, whereas in the normal female it runs straight forward ; on the 

 outer side of this fissure are two conspicuous spots — that in front oblong blackish, 

 reaching the fissure ; that behind it round reddish and at some distance from the 

 fissure. The latter spot is caused by the underlying spermatheca, the former by the 

 duct leading from it to the external aperture. Of all this the left half of the genital 

 area shews no trace. 



This careful description simply means that (externally)^ the spider 

 was wholly and completely male on the left side and female on the right, 

 the structures being strictly normal except for junctional distortion. It 

 is interesting to note that the careful examination of this spider revealed 

 the sexual differences in tarsus I which had previously escaped notice. 



2. As 1, hut one side imperfectly developed before, the other behind. 

 This is exemplified (according to my own reading of it !) by Falconer's 

 Maso sundevallii, — a British example captured by Dr A. Randell Jackson, 

 time and place unknown. But I have not seen the actual specimen, and 

 Falconer's opinion is different. I quote his brief description : 



1 This qualification is to be understood throughout this paper. No dissections have 

 been made of any of the gynandromorphs here enumerated. 



