BEGINNING OF NERVES. 



313 



process, whatever it may be, a process of physiological induction^ we 

 may apply a similar name to a process which seems closely analogous 

 to, if it is not really identical with, the process we are now considering. 

 I refer to some highly reQiarkable observations w^hich were published a 

 year or two ago in Mr. Darwin's work on " Insectivorous Plants." It is 

 there stated that, while looking at a linear series of excitable cells with 

 the microscope, Mr. Darwin could observe the passage of a stimulus 

 along the series, the protoplasm in the cells immediately stimulated first 

 undergoing aggregation, then the protoplasm in those next adjacent 

 doing the same, and so on. Now, the protoplasm in each cell was sepa- 

 rated from the protoplasm in the adjacent cell by the walls of both the 

 cells ; yet, notwithstanding there was no observable anatomical conti- 

 nuity between these masses of protoplasm, a disturbance set up in any 

 one of the series of masses immediately set up, by some process of phys- 

 iological induction, a sympathetic disturbance in the immediately adja- 

 cent masses. 



This, then, is one case that seems to be comparable with the case 

 of physiological induction in the nerve-fibres of Aurelia, and I think it 

 may be well for physiologists to keep awake to the fact that a process 

 of this kind probably takes place in the case of these nerve-fibres. For 

 it thus becomes a possibility which ought not to be overlooked, that 

 in the fibres of the spinal cord, and in ganglia generally, where his- 

 tologists have hitherto been unable to trace any anatomical or struct- 

 ural continuity between cells and fibres, which must nevertheless be 

 supposed to possess physiological or functional continuity — it thus 

 becomes a possibility that in these cases no such anatomical continuity 

 exists, but that the physiological continuity is maintained by some 

 such process of physiological induction as probably takes place among 

 the nerve-fibres of Aurelia. 



Before quitting the histological part of the subject, it is desirable 

 to state that at about the same time as Mr. Schafer's work was com- 

 municated to the Royal Society, tAvo other papers were published in 

 Germany on the same subject. One of these papers was by Messrs. 

 Hertwig, and the other by Dr. Eimer. Both memoirs display a large 

 amount of patient research, and describe the character and distribution 

 of the nervous tissues in various species of Meclusce. These authors, 

 however, do not describe the nervous network which has been described 

 by Mr. Schafer. I may add the interesting fact that the nervous tis- 

 sues in Medusoi appear to be exclusively restricted to tlie body-layer 

 which is called the ectoderm, and which is the structural homoloffue of 

 that body-layer in which the nervous tissues of all the higher animals 

 are known to have their origin during the life-history of the embryo. 



Proceeding now to state some further results of various physio- 

 logical experiments, I shall begin with the department Stimulation. 

 And first to take the case of a physiological principle which I observed 

 in the jelly-fish, and which has also been found to run through all ex- 



