422 G. H. Parker. 



animals, as well as the swimming-plates of the ctenophores, still 

 possess the power of neuroid transmission. 



IV. SUMMARY. 



1. In Mnemiopsis and Pleurobrachia the swimming-plates 

 normally beat metachronally beginning at the aboral ends of the 

 rows. 



2. In Mnemiopsis the two rows of plates belonging to the same 

 quadrant of the animal's body beat in unison. In Pleurobrachia 

 this is also often true, but all eight rows in this ctenophore may 

 beat independently. 



3. The propagation wave ("Reizwelle" of Engelmann) shows 

 scarcely any evidence of reversal in Mnemiopsis, but often 

 reverses in Pleurobrachia. 



4. Reversal of the effective stroke of the plates was never 

 observed in Mnemiopsis or in Pleurobrachia. 



5. On cutting a row of plates in Mnemiopsis transversely, 

 the oral part quickly recovers and begins beating, but not in unison 

 with any other part; the aboral part also recovers soon and beats 

 in unison with the other row of its quadrant. 



6. A single isolated plate will beat if it retains a small amount 

 of basal protoplasm. 



7. Plates without basal protoplasm will not beat, though they 

 are not dead. 



8. Loss of a plate in a row does not prevent the passage of 

 a wave even in Mnemiopsis where the cilia on the rows do not 

 always form continuous bands. 



9. When the plates on part of a row in Mnemiopsis are re- 

 strained from moving, an impulse to plate movement may still 

 be transmitted. 



10. Cooling a part of a row with water at 5° C. will bring the 

 movement of the plates to a standstill, but not interrupt trans- 

 mission. 



11. Stretching part of a row will cause local cessation ot move- 

 ment, but will not interrupt transmission. 



12. The metachronism of the plates in ctenophores cannot be 

 explained as a result of the mechanical influence of one plate on 

 its neighbor, but the facts observed necessitate the assumption of 

 a deep-seated transmission from cell to cell, nerve-like in character. 



