340 Mr. J. Blackwall on certain PecuUaritles in the 



XLVII. — A Concise Notice of Observations on certain Pecu- 

 liarities in the Structure and Functions of the Araneidea. 

 By John Blackwall, F.L.S. 



Much diversity of opinion being entertained by eminent zoo- 

 tomists and physiologists with regard to the structure and 

 function of certain organs common to spiders belonging to 

 several genera, which are situated near the extremity of the 

 inferior surface of the abdomen, immediately before the spin- 

 ning-mammulae, I availed myself of recent visits of a friend, 

 Mr. William Statham, to inspect under his excellent binocular 

 microscope the parts in question, carefully prepared for the 

 purpose by himself. When efficiently illuminated and viewed 

 with a magnifying-power of about 125 diameters, they were 

 distinctly perceived to be provided with very numerous and 

 exceedingly delicate spinning-tubes, completely establishing 

 the accuracy of the conclusion at which I had previously 

 arrived by minute investigation, namely that the parts consti- 

 tute an additional or fourth pair of spinners united throughout 

 their entire length*. 



The spiders submitted to examination were Ciniflo atrox^ 

 C. similis, and Ergatis viindissima. Between the proximate 

 extremities of the fourth pair of spinners in the first two spe- 

 cies there is a distinct septum ; but in Ergatis viridissima, 

 Mithras j)aradoxus^ and some other small spiders provided 

 with the additional spinners no septum is apparent, the entire 

 area formed by their contiguous extremities being amply sup- 

 plied with spinning-tubes. 



The conjoined spinners composing the fourth pair are mov- 

 able, and, when in action, present their extremities to the 

 calamistra, which in passing over them draw out and card the 

 excessively fine filaments proceeding from the spinning-tubes 

 into the two delicate pale blue bands that enter into the com- 

 position of every flocculus in the complex snares of Ciniflo 

 atroXj C. similis, and C.ferox. 



The small spiders, the proximate extremities of whose addi- 

 tional spinners are withou.t any definite mark of distinction, 

 have the calamistrum (situated upon a ridge on the abdominal 

 side of the upper surface of the metatarsal joint of each poste- 

 rior leg) usually composed of a single row of curved movable 

 bristles ; but the calamistrum of the larger species of Ciniflo 

 commonly consists of two parallel rows of fine spines. 



I may here remark that the calamistra are frequently much 



* Transactions of the Linnean Society of London, vol. xviii. p. 223 

 et seq. 



