74 ADRENALIN IN ANNELIDS 



and Smirnow^ has shown that such cells are innervated by nerve fibers 

 which are otherwise indistinguishable from those which run to the 

 sympathetic nerve cells lying with them. Further back in the ver- 

 tebrate kingdom the distribution becomes still more diffuse and the 

 sympathetic nervous system becomes less and less defined and more 

 and more replaced by a diffuse system of chrome-staining cells 

 arranged segmentally throughout the body. 



A definite sympathetic nervous system has been long known in the 

 case of the elasmobranch fishes, but it is only comparatively recently 

 that the researches of Giacomini and others have definitely demon- 

 strated its presence in the other groups of fishes. Giacomini finds a 

 definite double sympathetic chain present in the Dipnoi,^ but in the 

 Ganoidei^ and Teleostei^ he was able to find only an irregular system 

 of nerve cells distributed along the cardinal veins. In the cyclo- 

 stomes^ the representatives of the sympathetic nervous system are 

 still more scanty, being certain nerve cells which are occasionally to 

 be found around the cardinal veins. In all these groups of fishes 

 there is again an intimate relationship between the sympathetic nerve 

 cells and diffusely distributed chrome-staining cells. The presence 

 of adrenalin in the latter cells was demonstrated by Vincent in the 

 elasmobranchs,' and in a previous paper I^ gave reasons for believ- 

 ing that the chrome-staining tissue of the cyclostome, Petromyzon 

 fluviatilis, also contained adrenalin. An extract of such tissue caused a 

 rise of blood pressure in the cat, which was in every way similar to 

 that caused by a small dose of adrenalin. The conclusion may there- 

 fore be drawn that chrome-staining tissue, wherever found among 

 vertebrates, secretes adrenalin, and the presence of a sympathetic 

 nervous system and an adrenahn-secreting system may be considered 

 to have been established throughout the vertebrate kingdom. The 

 two systems are in every animal most intimately connected physio 



* Smirnow, A., Arch. mikr. AnaL, 1890, xxxv, 416. 



' Giacomini, E., Aiti Accad. Lincei, Rendiconti, 1906, xv, series 5, 394. 



* Giacomini, E., Monitore zool. ital., 1904, xv, 20. 



^ Giacomini, E., Monitore zool. ital., 1902, xiii, 183. 

 ® Giacomini, E., Monitore zool. ital., 1902, xiii, 143. 

 "> Vincent, S., Proc. Roy. Soc. London, 1897, Ixi, 64. 

 8 GaskeU, J. F., J. Physiol, 1912-13, xliv, 59. 



