J. F. GASKELL 75 



logically and anatomically. The work of Kohn' has also shown how 

 closely their evolution in the vertebrate is paralleled by their embry- 

 ological development in the mammal. 



A search for the origin of the two systems must therefore be pursued 

 in the invertebrate kingdom. If it is allowed that the presence of a 

 yellow coloration after fixation with a chrome salt in certain cells, 

 which have been called chromaffin cells, occurs among vertebrates 

 only in cells which contain adrenalin, the presence of such a reaction 

 in cells of invertebrates is presumptive evidence that the latter are 

 also adrenalin-secreting cells. The first discovery of chromaffin cells 

 in the invertebrate was made by Poll and Sommer^^* who described 

 the occurrence of the reaction in certain cells of the central nervous 

 system of the leech, Hirudo medicinalis. PolP^ has since extended 

 this observation by finding similar cells in certain other annelids. 

 The only other observation is that of Roaf and Nierenstein^^ who ex- 

 tracted an adrenalin-like body from certain tissues lying in the walls 

 of the branchial chamber of the mollusk, Purpura lapillus. Subse- 

 quently Roaf^^ located this secretion to certain cells which gave a 

 chromaffin reaction. As the Mollusca are not held to be on the direct 

 line of vertebrate descent attention has been confined to the annelid 

 kingdom. 



A representative selection of annelids was examined at the Zoolog- 

 ical Station of Naples, and a detailed description of the results has 

 been given in my paper pubHshed in 1914.^* Among the Hirudineae 

 chromaffin cells have been found in the ganglia of the central nervous 

 system in all species investigated. Seventeen different animals of the 

 polychaete group were examined but in fifteen of these no trace of 

 chromaffin cells could be found; in the remaining two, Aphrodite 

 aculeata and Eunice gigantea, small chromaffin cells were present. 

 Lumhricus herculeus, the only oligochaete investigated, also possessed 



9 Kohn, A., Arch. mikr. Anat., 1903, Ixii, 263, 

 i« Poll, H., and Sommer, A., Arch, physiol., 1903, 549. 



" Poll, H., in, Hertwig, O., Handbuch die vergleichende und experimentelie 

 Entwicklungslehre der Wirbeltiere, Jena, 1906, iii, pt. 1, 603. 

 12 Roaf, H. E., and Nierenstein, M., /. Physiol, 1907, xxxvi, p. v. 

 1^ Roaf, H. E., Quart. J. Exp. Physiol., 1911, iv, 89. 

 " Gaskell, J. F., Phil. Trans. Roy. Sac. London, Series B, 1914, ccv, 153, 



