APPENDIX 417 



to me that by operating on animals intermediate in organisa- 

 tion between the 'Hydra and the worm it might be possible 

 to discover traces of the commencement of the nervous system 

 in the animal kingdom. 



For in the worm we have — and this is the reason why we 

 can divide it with the result mentioned into its component 

 parts (segments) — a nervous system which is repeated in 

 every segment — a nerve-cord which runs along the ventral 

 side of the animal, and in every segment enlarges into a 

 ganglion, and each of these ganglia can in some sort be 

 reo-arded as a brain of the animal. It is the same with the 

 other organs — each is repeated in every segment of the worm, 

 so that the animal is to be regarded as a composite of several 

 parts, each of which is a whole complete in itself. But this 

 worm was developed from a sim^^le unsegmented larva. 



For my first experiments I took various kinds of jelly- 

 fishes. I will here only mention those which I made on the 

 large kinds. Many of you know these creatures, at least 

 those who live at the sea-side or visit watering-places. Some 

 kinds of them are at times a great annoyance to bathers, for 

 when they come in contact with the skin they cause great 

 irritation by means of small glands they possess which send 

 out minute stings charged with an acid. Such a jelly-fish may 

 be compared to an umbrella if we suppose that the latter 

 is made of a watery gelatinous substance, and that instead 

 of the wires which form the ribs of the umbrella there are 

 canals running in the jelly which meet in a common chamber 

 at the apex of the umbrella, the stomach of the animal, and 

 open to the exterior through the stick of the umbrella by an 

 aperture at its lower end, the mouth. Eound the margin of 

 this umbrella, at regular distances, there exist several small 

 bodies, which have long been conjecturally regarded as sense- 

 organs, the so-called marginal bodies, each one at the end of a 

 canal. 



2 E 



