260 



SCIEA T CE-GOSSIP. 



palpi are two- or threefold, viz., that of touch, of 

 prehension, and as a means for conveyance of fluid to 

 its proper destination. To describe minutely the 

 details of their several parts is beyond my province ; 

 I wish now to point out in a general way some 

 remarkable features presented by these organs. The 

 first to strike a novice are the curious instruments of 

 prehension with which they are often furnished. In 

 certain species of Tegenariae the terminal joints are 

 developed into pincer-like processes, one pincer 

 fitting into its opposite as into a sheath, thus closely 

 resembling the mandibles of a parrot. The pair 

 forms a very efficient instrument for holding on to 

 the hairy body of the female. In another, not very 

 common, species the last joint is furnished with two 

 hooks, so long and sharply pointed that their use is 

 at once seen to be to pierce the tough integument of 

 the female. 



Various modifications of these instruments are to 

 be found in different families. The most remarkable 

 of all the appliances with which these palpi are 

 supplied are the filaments that occur in the terminal 

 joint of many species. These filaments are often six 

 to eight times the length of the spider's whole body. 

 As seen after preparation for the microscope, they 

 are ribbon-like, furnished throughout their whole 

 length with a channel, canal, or duct for the convey- 

 ance of the spermatic fluid. I have never seen these 

 organs other than as flattened threads, and these, 

 when not in use, are, so far as my observations have 

 gone, stowed away in their receptacle, not in spiral 

 coils, like the mainspring of a watch, nor yet like 

 the familiar spiral fibre of plants, but are folded upon 

 themselves in zigzag fashion, like the arm of the old- 

 fashioned "lazy-tongs." 



It may be said that, as a general rule, the length 

 of these filaments is determined by the length of 

 the spider's legs. In the fat, short-legged spiders 

 these ribbons, where they exist, are short ; in the 

 very long-legged ones, where the legs far exceed 

 those of the longest-legged harvest spiders, they 

 are of astonishing length. My mind was for a long 

 time considerably exercised to discover the reason 

 for the wonderful development of these appendages. 

 A solution of the mystery presented itself when I 

 was once watching the antics of a pair of extremely 

 long-legged spiders, which appeared to be engaged 

 in a frolic, ludicrously resembling a fencing bout, 

 though the principals never came to close quarters. 

 Here, then, was the explanation sought — this was 

 their courtship. Owing to their extremely long legs, 

 the male was never able to more closely embrace his 

 mate. Without doubt he is able to throw out the 

 long filaments towards the female, but, being so 

 microscopic in their tenuity, they are invisible to a 

 human observer, unless, possibly, some sun ray 

 should reveal them. How the creature contrives to 

 steer the whip-like filaments through the entangle- 

 ment of moving legs I cannot pretend to explain, 

 but feel confident that my solution is a correct one. 

 In some species, notably the genus Salticus, the 



instrument can no longer be termed a filament, 

 scarcely exceeding in length the receptacle in which 

 it is contained ; and, seeing that kindred species are 

 destitute of these ribbon-like appendages, it is very 

 remarkable that they should possess them. 



In this subject I have briefly indicated what may 

 possibly prove to be one of interest, not only to the 

 young naturalist, but also to the more advanced, 

 whose observations may hitherto have been confined 

 to the general aspect of the male spider and his 

 curious palpi. 



Woodville, Greenhouse Lane, 

 Painswick, Gloucestersh ire. 



BRITISH FRESHWATER MITES. 



By Charles D. Soar, F.R.M.S. 



(Continued from page 234.) 



GENUS ACERCUS KOCH. 



Body. — Soft-skinned. The characteristics of the 

 females are very similar to those of Curvipes. In the 

 males the epimera is fused into two groups, and the 

 last segment of each leg of the fourth pair is much 

 modified. Numerous discs on the genital plates. 



None of the species of this genus are common. 

 There are several more species known on the Con- 

 tinent, so additional species may yet be recorded for 

 Britain. 



Acercus ligulifer Piersig, 1897. 

 Male. — Body oval in form. Length about 

 0.64 mm. Breadth about 0.48 mm. Colour a straw- 



Fig. 1. Acercus ligulifer. 

 Ventral surface. Male. 



Fig. 2. A. ligulifer. 

 Tarsus of fourth leg. 



yellow, with brown markings. Eyes are large and 

 prominent. On the margin of the body are several 

 short hairs. 



Legs. — First pair about 0.40 mm. Fourth pair 

 about 0.58 mm. They are well supplied with hairs. 

 The tarsi of the first two pairs of legs are wide and 

 thick. On the third pair they are thin and small. 

 On the fourth pair the tarsi are quite a different 

 Structure from any of those we have previously con- 

 sidered in having two bristles bent into hook-shape 



