154 MR. J, BLACKWALL ON SOME EEMAEKABLE TACTS 



tumours ; and it is common to see a peculiar white appearance, 

 often in rings, on the interior of the stomach. These portions are 

 denser than the ordinary mucous surface, and often slightly ele- 

 vated. Under the microscope they are fibro-granular. It is pro- 

 bable that they originate in some former parasitic inroads. 



A succinct Eeview of recent Attempts to explain several remark- 

 able Tacts in the Physiology of Spiders and Insects. By John 

 Blackwall, P.L.S. 



[Read AprU 2, 1863.] 



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

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

 internal 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 abdomen. This hypothesis, based on zoo- 

 tomical considerations, being directly opposed to the conclusion 

 arrived at by myself from numerous carefully conducted experi- 

 ments, merits an impartial examination. 



After having briefly stated the general results obtained by his 

 dissection of several species of spiders, and minutely described the 

 organization of the internal vessels that elaborate the material 

 which, on issuing from the papillae connected with the spinners, 

 forms filaments of extreme tenuity, Mr. Meade remarks, " I 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 on the ducts of the membranous sacs, and 

 the fibrous tissue surrounding the glands themselves, I think that 

 they 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 muscular fibres, which run in a parallel direction down the 

 middle of the abdomen quite into the interior of the spinnerets, 

 and surround the termination of the ducts, also assist in this ob- 

 iect ? They are not attached to the tegumentary coverings of the 

 spinnerets like the other muscles, and cannot therefore be for the 



* Keport of the Twenty-eiglith Meeting of the British Association for the 

 Advancement of Science, p. 157. 



