106 THE ELEMENTARY NERVOUS SYSTEM 



pedote medusae, unlike those without the veil, are com- 

 monly characterized by a double band of nervous tissue 

 encircling the margin of their bells. On the other hand, 

 the subumbrellar nerve-nets and muscle bands are essen- 

 tially alike in both the craspedote and the acraspedote 

 forms. 



The physiology of the neuromuscular mechanism of 

 jellyfishes was independently investigated by Eimer and 

 by Romanes. In 1873 Eimer presented before the Physi- 

 kalisch-medicmische Gesellschaft in Wiirzburg a prelim- 

 inary communication on his researches in this field, a pub- 

 lished statement of which appeared in 1874, the year in 

 which Romanes published his first brief note on the sub- 

 ject. Romanes' two extended papers appeared, one in 

 1877 and the other in 1878, the year in which Eimer 's 

 monograph came from press. The results of these two 

 investigators were in essential agreement. In the main 

 they entirely justified the view subsequently worked out 

 by histological means that jellyfishes possess on their 

 subumbrellar surfaces an intricate nerve-net. 



It was found that if the eight marginal bodies of such 

 a jellyfish as Aurelia were excised, the pulsations of the 

 bell, for the time being at least, ceased. If all but one 

 were excised, the pulsations continued and emanated from 

 the one remaining marginal body. Such an animal 

 formed a very convenient preparation on which to study 

 the course taken by the impulse to contraction. 



Both Romanes and Eimer showed that the bell of a 

 jellyfish could be cut into a most complex pattern without 

 interfering with the passage of the wave of contraction 

 throughout its whole extent. If the single marginal body 

 on a prepared bell of Aurelia is stimulated, a contraction 

 appears in its immediate vicinity and spreads as two 



