The present part of this memoir contains descriptions of four additional specimens of Osmundites which have been obtained from various sources.

We are indebted to Dr G. Nathorst for the material of Osmundites spetsbergensis, Nathorst MS., which was first collected by Dr G. Nordenskiöld on the Spitzbergen Expedition of 1890 at Nordenskiöldsberg, and subsequently by Dr B. Högbom in 1910 at Van-Mijensberg, Spitzbergen.

Our thanks are also due to Dr A. Rothpletz, Director of the Geologisch-palaeontologische Staatssammlung, München, for kindly placing in our hands the type specimen of Osmundites Carnieri, Schuster, for investigation and redescription.

In view of the differences observed in the pharmacological action of tetra-methyl- and tetra-ethyl-ammonium chlorides, it seemed of interest to investigate the actions of the methyl-ethyl-ammonium compounds. The chlorides of these compounds—namely, tri-methyl-ethyl-ammonium chloride, di-methyl-di-ethyl-ammonium chloride, methyl-tri-ethyl-ammonium chloride—were kindly prepared for me by Dr J. E. Mackenzie, who has published the mode of preparation and the analysis of them.

The only references I have found to the pharmacological action of the members of this series are brief statements by Tappeiner and Boehm. Tappeiner says that tri-ethyl-methyl-ammonium chloride, unlike tetra-methyl-ammonium chloride, does not produce temporary paralysis of the respiration; Boehm that tri-methyl-ethyl-ammonium chloride, like tetra-methyl-ammonium chloride, causes contracture of an isolated frog's muscle when a solution is applied to it.

This section under the above designation was first established by Pax in Engler's Bot. Jahrb., x, 205 (1889). The species chosen as representative of the section was P. nivalis Pall. This species with its numerous and widespread immediate allies affords an admirable centre for an exposition of the members of the section. The original definition of the sectionis still reasonably adequate, but its clarity was somewhat obscured by the admission of several species which indubitably belong elsewhere. Of the nine components quoted by Pax, five must be removed—P. sikkimensis and P. secundiflora, as well as the American P. Rusbyi and its two associates. In his Monograph (1) published in 1905 Pax made certain additions and corrections. The number of species indicated as within the section was increased to 15. He removed P. Rusbyi to what is now Candelabra, but P. Cusickiana and P. angustifolia were retained; so also were P. sikkimensis and P. secundiflora. On good grounds were included P. pumila, P. Aitchisonii, and P. eximia, but dubiously P. pulchella and P. Prattii. Correctly in our opinion came in P. Maximowiczii and its two allies P. szechuanica and P. tangutica.

Elsewhere two of the present authors (Davies and Francis, 1941) have expressed theopinion that a specialised cardiac conducting system, consisting of nodal and Purkinje fibres, is a newly evolved one in birds and mammals. The general morphology and topography of this system in the heart of the bird (Davies, 1930 a, 1930 b) is similar to that in the heart of the eutherian mammal, and we have postulated (Davies and Francis, 1941) that the system has undergone parallel evolution in these two classes of homoiothermal vertebrates in response to functional requirements, and that in particular its presence can be correlated with the rapidity of the heart-rate in proportion to its size. On the other hand, Keith and Flack (1907), Keith and Mackenzie (1910), and Mackenzie (1913) maintain that the sinu-atrial node, atrio-ventricular node, and atrio-ventricular bundle of the mammalian heart are remnants of more extensive tissues of similar structure in the hearts of lower vertebrates. They trace the evolution of the conducting system of the mammalian heart from a simpler and more definite form which they described in the fish, and state that as one ascends the animal scale the concentration and reduction of nodal tissue becomes more marked.