RECORD OF CURRENT RESEARCHES, ETC. 919 



Origin of the Nervous System. — The following is from Mr. F. M. 

 Balfour's address to the Department of Anatomy and Physiology, at 

 the recent meeting of the British Association : — 



" The general features of the origin of the nervous system, which 

 have so far been made out by means of the study of embryology, are 

 the following : — 



1. The nervous system of the higher Metazoa has been developed 

 in the course of a long series of generations by a gradual process of 

 differentiation of parts of the epidermis. 



2. Part of the central nervous system of many forms arose as a 

 local collection of nerve-cells in the epidermis, in the neighbourhood 

 of rudimentary organs of vision. 



3. Ganglion-cells have been evolved from simple epithelial cells 

 of the epidermis. 



4. The primitive nerves were outgrowths of the original ganglion- 

 cells ; and the nerves of the higher forms are formed as outgrowths 

 of the central nervous system. 



The points on which embryology has not yet thrown a satisfactory 

 light are : — 



1. The steps by which the protoplasmic processes, from the primi- 

 tive epidermic cells, became united together so as to form a network 

 of nerve-fibres, placing the various parts of the body in nervous com- 

 munication. 



2. The process by which nerves became connected with muscles, 

 80 that a stimulus received by a nerve-cell could be communicated to 

 and cause a contraction in a muscle. 



Eecent investigations on the anatomy of the Coelenterata, especially 

 of jelly-fish and sea-anemones, have thrown some light on these points, 

 although there is left much that is still obscure. 



In this country Mr. Romanes has conducted some interesting 

 physiological experiments on these forms ; and Professor Schiifer has 

 made some important histological investigations upon them. In 

 Germany a series of interesting researches have also been made on them 

 by Professors Kleinenberg, Glaus, and Eimer, and more especially by 

 the brothers Hertwig, of Jena. Careful histological investigations, 

 especially those of the last-named authors, have made us acquainted 

 with the forms of some very primitive types of nervous system. In 

 the common sea-anemones there are, for instance, no organs of special 

 sense, and no definite central nervous system. There are, however, 

 scattered throughout tlie skin, and also throughout the lining of the 

 digestive tract, a number of specially modified epithelial cells, which 

 are no doubt delicate organs of sense. They are provided at their 

 free extremity with a long hair, and are prolonged on their inner side 

 into a fine process, which penetrates the deeper part of the epithelial 

 layer of the skin or digestive wall. They eventually join a fine net- 

 work of protoplasmic fibres, which forms a special layer immediately 

 within the epithelium. The fibres of this network are no doubt 

 essentially nervous. In addition to fibres there are, moreover, present 

 in the network, cells of the same character as the multipolar 

 ganglion-cells in the nervous system of Vertebrates, and some of these 



