46 Fads in the Phjsiology of SjAders ami Insects. — Blackwell. 



A Succinct Review of Recent Attempts to Explain Several Remarlcable Facts 

 in the Physiology of Spiders and Insects. By John Blackwell, 

 F. L. S. [From Jour, of Pro. of Linnrean Society, vol. vii., p. 154. 

 My friend, Mr. Meade, in his valuable report " On some Points in 

 the Anatomy of the Araneidea, or true Spiders, especially on the In- 

 ternal Structure of their Spinning Organs," has been induced by his 

 researches to adopt the opinion that these animals can propel from their 

 spinners, to a considerable distance, fine lines, formed of the viscid fluid 

 secreted by appropriate organs, situated in the interior of their abdo. 

 men. This hypothesis, based on zootomical considerations, being di- 

 rectly opposed to tlie conclusions arrived at by myself, from numerous 

 carefully conducted experiments, merits an impartial examination. 



After having briefly stated the general results obtained by his dis- 

 section of several species of spiders, and minutely described the organ- 

 ization of the internal vessels that elaborate the material which, on 

 issuing from the papillse connected with the spinners, forms filaments 

 of extreme tenuity, Mr. Meade remarks, " 1 have now arrived at the 

 most interesting, but most difficult part of my task, viz., the question 

 whether there is anything in the structure of the silk-forming organs 

 that will decide the question as to the power of spiders to eject their 

 threads to a distance. Looking at the strong fibrous coat ou the ducts 

 of the membraneous sacs, and the fibrous tissue surrounding the glands 

 themselves, I think tliatthey must possess a powerful contractile power, 

 which may also be increased by the muscular coat of the integument, 

 enabling the spider to compress its abdomen. May not the striated 

 bands of inuscular fibers, which run in a parallel direction down the 

 middle of the abdomen quite into the interior of the spinnnerets, and 

 surround the termination of the ducts, also assist in this object? They 

 are not attached to the tegumentary coverings of the spinnerets like 

 the other muscles, and can not, therefore, be for the purpose of moving 

 these processes ; their action must be to draw the spinnerets inward." 

 Such is the evidence supplied by dissection in support of the opinion 

 that spiders can forcibly eject their lines to a distance. 



Now, it is manifest, from well known physiological facts, that the 

 muscles distributed to the spinning organs perform various functions : 

 the office of some being to give motion to those'parts, of others, to close 

 either the minute aperture in the dilated base of the tubular papilla?, 

 or that of the fine ducts which terminate the vessels that secrete the 

 fluid employed by spiders in the process of spinning, as its issue from 

 the papilliB can be instautaneously prevented at the will of the ani- 

 mals ; others, moreover, must possess a contractile force sufficient to 



