EXPERIMENTS ON BEROE 



the independent activity of the pieces followed very quickly 

 and from the first with greater certainty. Beroe shows 

 therefore, with respect to the nervous system, a much more 

 embryonic condition than the Medusa investigated. 



Experiment B. I cut through one of the rows of plates of 

 a Beroe and the subjacent tissue, with a pair of scissors, at a 

 point about 2 cm. below the aboral pole, at the level of x in 

 Fig. 4. The movement of the plates ceased for a moment in 

 the whole animal. Then the movement recommenced first 

 in the uninjured rows of plates, next in the upper portion of 

 the divided row, a, and lastly in the lower portion of the same, 

 b. After it was re-established everywhere, it appeared that the 

 motion in the two portions of the row operated upon, above 

 and below the cut, went on independently. Both in a and b 

 it was rapid, in I it could even attain greater rapidity than 

 in a. In both portions the direction of the motion was 

 towards the mouth, and the movement consisted in the same 

 rapid succession of waves as in the uninjured animal. The 

 fact that the waves in the two sections were independent was 

 established not only by mere observation, but more certainly 

 by the following experiment : when I lightly touched the 

 upper portion with a needle the movement ceased in it for a 

 moment, while in b it went on as before and similarly the 

 movement could be stopped in the lower portion while it 

 continued in the upper. Immediately after the operation, the 

 waves in a proceeded from the aboral pole to the incision, 

 while in I waves quite independent of these in a began at the 

 incision and passed towards the mouth ; but eight hours after- 

 wards it appeared to the eye as if the connection between a 

 and b was re-established, as if continuous waves beginning at 

 the aboral pole were propagated through a across the incision 

 to b and then to the mouth. It was found, however, when b 

 was touched with a needle that the movement in this portion 

 was interrupted, but not in a. Thus a certain degree of 



