TRANSACTIONS OF SECTION D. 773 



The leaves of mosse? are therefore seen to have a function differing- very greatly 

 from that of the vascular plants ; while the apophysis of the sporophyte has 

 exactly the same functions as the leaves of the vascular plants. 



SaB-SECTiox PHYSIOLOGY. 



1. Report of the Committee for the Investigation of the Secretion of Urine. 

 See Reports, p. 131. 



2. Report of the Committee appointed for the purpose of investigating the 

 Fhijsiology of the Lijmpliatic System. — See Reports, p. 145. 



3. Oil the Development of the Boots of the Nerves and on their PropagaAion 

 to the Central Organs and to the Periphery. By Professor His. 



It is about fifty years since Theodor Schwann, in his fundamental work on the 

 animal cell, gave out the opinion that nervous fibres are formed b}' the connection 

 of rows of cells. This opinion has for a long time prevailed among all liistologists, 

 and has also been adopted by the eminent embryologist that English science lost 

 at so early an age, the late Professor Balfour, and by Prolessor M. Marshall and 

 others. 



Besides this older theory and that of Professor Hensen, which I can omit 

 to-day, there is auother, first brought np by Messrs. Bidder and Kuptfer in the 

 year 1858. These inquirers considered nervous fibres as direct outgrowths from 

 central cells. I myself have been led by mj^ own inquiries a long time ago 

 to adopt this opinion, and I came, moreover, to the conviction that, while motor 

 fibres grow out from the cells of the spinal cord and of the brain, sensitive fibres 

 have their issue from the cells of the ganglions. In the last six years I have had 

 the opportunity of verifying this supposition, and I should think that on this point 

 discussion is no more possible. No motor cylinder axis, for instance, issues from 

 a row of cells ; everyone comes only from one cell situated in the spinal cord or in 

 the brain. 



The observations of Professor Balfour, of Professor Marshall, and others on 

 cells in the path of motor nerves are completely true ; it is also true that these 

 cells are in some way engaged in the formation of nerves, but they have nothing 

 to do with the cylinder axis ; they form only the accessory parts of the nerves, the 

 neurilemma and the sheath of Schwann. In the dog-fishes these acces.sory cells are 

 very richly developed, while in the human embryo they appear slowly. Sections 

 of human embryos are, therefore, much better suited' to all the studies of the 

 formation and the propagation of nervous fibres than the sections of dog-fishes 

 and of many other vertebrates. 



In the human embryo the first nervous fibres are to be seen during the fourth 

 week, and the fibres emerging from the spiual cord appear a little Eoouer than 

 the fibres coming out of the ganglions. At this time there can be distinguished 

 in the spinal cord an outer and an inner layer of cells. The inner layer is more 

 compact, and it only contains karyokinetic figures, while every cell of the outer 

 layer sends out one fibre or one cylinder axis. The fibres of the dorsal half go 

 forwards, forming partly the white commissure, partly longitudinal cords. The 

 fibres of the ventral half run to the surface of the spinal cord; they pass out and 

 unite so as to form the motor roots. Every root is formed by a certain number 

 of fibres, all issuing from single cells of the corresponding floor of the spinal 

 cord. There are in this earl}- period no ramified processes of tlie spinal cells. 



The brain part of the medullary tube shows also a separation between an 

 outer and an inner layer of cells, and leaving out of cou.*ideration the fore-braia 

 that we actually can pass over, every one of the outer cells seems also to send out 



