420 G. H. Parker. 



('80, p. 5), though on insufficient grounds, for no one has ever 

 demonstrated that nerves are connected with these plates. Engel- 

 mann ('87, p. 442) has used the expression "innervated" in 

 reference to the rows of swimming-plates, but it is perfectly 

 evident from other statements in his account (p. 440) that this 

 term is used in a physiological sense and not in an anatomical 

 one, and that he consistently adheres to his original idea ('79, 

 p. 395) of epithelial transmission. Chun ('80, p. 173) made 

 perhaps the best brief statement of the mechanism of transmission 

 in ctenophores when he declared that the rows of epithelial cells 

 served as nerves. It is in my opinion an open question whether 

 in any instance cilia are really controlled by nerves. Such a con- 

 trol is denied by Verworn ('95, p. 251), though Piitter ('03, p. 98) 

 in his recent survey of the whole subject of ciliary activity states 

 that in the larvae of certain annelids such control occurs. It seems 

 to me that Putter's grounds are insufficient for such a conclusion; 

 but, however this question may stand for annelids, in the cteno- 

 phores not the least histological evidence has ever been advanced 

 to show that their rows of plates are accompanied by nerves. 

 Samassa ('92, p. 226), who has studied this matter with care, 

 denies that ctenophores have any nervous system properly so 

 called and points (p. 230) to the epithelial bands in Beroe as the 

 transmitting organs. There thus seems to be good reason for 

 believing that the epithelial cells on the rows of swimming-plates 

 in ctenophores transmit impulses that control the metachronism 

 of these plates; in other words the neuroid theory, contrary to the 

 statement made by Verworn ('90, p. 175), is tenable. Such a 

 conclusion is entirely consistent with the results of Gruetzner 

 ('82) and of Kraft ('90) in their experiments on transmission in 

 the ciliated epithelia of the higher animals, for both investigators 

 found it necessary to assume a deep-seated cellular transmission 

 to explain the spread of ciliary disturbances in active and in quies- 

 cent fields of cilia. 



Although the results of my experiments make me confident that 

 the metachronism of the swimming-plates of ctenophores is due to 

 neuroid transmission, I do not believe that the facts warrant the 

 extreme position taken by Engelmann ('87, p. 440) that no form 

 of mechanical transmission obtains. It seems to me much more 

 likely that, as Chun ('80, p. 174) has declared, mechanical action 

 is a subordinate though real factor in transmission. In my 



