OCR Text |
Show 1897.] MK. R. I. POCOCK ON ETHIOPIAN SPIDERS. 743 the young stages of a species in which, when adult, the pads are complete, that is show no median divisional line of normal hairs, be examined, it will be found that at first the tarsi are clothed with setae, and these later on become intermixed with scopular hairs. As the animal increases in size the scopular hairs increase in number, gradually spreading over the tarsus, and apparently replacing the normal setae. But the replacement does not take place at a uniform rate all over the foot; on tbe contrary, tbe pad, beginning at the sides, encroaches by degrees inwards, and, as a consequence, the last part to remain unoccupied is the middle line of the sole, which retains longest its primitive clothing of setae. In the second place, it will further be noticed that the tarsal pads do not reach their full development contemporaneously, the order of their appearance corresponding with the order of the legs from before backwards-the first tarsus being covered before the second, the second before the third, and the third before the fourth ; so that when the pads upon the first or second legs are complete, those on the fourth, or even the third, may still retain their divisional line " . . . " Hence it follows that the division of the scopulae may be nothing but a sign of immaturity . . ." and a species belonging to section a8 for example of the above table " will in its early days fall into the Ischnocoleae, a little later into the Chaetopelmateae, then into the Crypsidromeae." Nevertheless, species undoubtedly exist in which one or all of the tarsi retain throughout life the divisional band of setae ; but a study of such of these genera as have been available has convinced me that the groups based upon such a character are largely artificial, and that in a natural classification of the family, within one and the same group genera will be found either with all or none of the tarsal scopulae divided; a conclusion which might be expected if the law of the growth of the tarsal scopulae mentioned above be true. For the genera that present a baud of setae on the scopulae are merely a little less specialized than those that lose them. It is, moreover, interesting to observe that in this character the adults of species of small size often resemble the young of closely-allied but larger-sized species. In another paper* I endeavoured to show that most of the genera inhabiting the Oriental region fall into two families, named respectively the Ornithoctonidae and Selenocosmiidae ; but it has since appeared to me advisable to reduce these to the rank of subfamilies, and term them Ornithoctoninae and Selenocosmiinae. These subfamilies are based upon the possession of a peculiar form of stridulating organ lying between the mandible and maxilla, but the organ is quite different in the two groups. The genera presenting these organs also agree in a number of other features, not, however, sufficient in themselves to differentiate them from some of the African genera. The Selenocosmiinae contain the genera referred by Simon to 1 Ann. Mag. Nat. Hist. (6) xv. pp. 165-184 (1895). |