STUDIES ON THE ECTOPARASITIC TEEMATODES OF JAPAN. J I 



produced by a distj.nct external epithelium sucli as has-been described 

 by Pintner in the Cestodes, which then underwent degeneration, or 

 finally (3) it may be only the remnant of the walls of the original 

 cells whose internal part has been absorbed and which thus gave rise 

 to the cavity of the excretory vessel. As I have pointed out in my 

 paper just referred to, in the extreme case, viz., where the cells are 

 arranged in a single row, the last view reduces itself to the first ; and 

 in this case the term "intracellular" has been used by most writers on 

 the subject. Quite recently HaswelP^ has extended the application 

 of this term to the terminal sac of the excretory system of Temno- 

 ceph-ala, so that according to this author the main canals as well as the 

 terminal vesicles are wholly intracellular. The ground on which 

 these writers regard the cavity of the excretory vessels as inti'acellular 

 has been clearly stated by one of them — the one, as far as I know, 

 who used the tei-m for tlie first time — ; and to avoid any misinter- 

 pretation I shall quote his own words. He says,^' "In ziemlich 

 grossen Abstanden verdickt sich die Wand der grossen Canale 

 einseitig und enthalt einen deutlichen, ovalen Kern. An diesen ver- 

 dickten StelJen inserirt sich stets je ein Biischel viel langerer Cilien. 

 Die Kerne sind so weit voneinander entfernt, dass auf eine langere 

 Strecke je eine einzige Zelle die Wand der grossen Canale bUdet ; mit 

 anderen Worten, diese Canale sind intracellular, sie stellen, durch- 

 bohrte Zellen dar." From this it is I think very clear that the 

 excretory vessels are called intracellular only because the nuclei are 

 never found more than one in the same section, but separated from one 

 another by wide intervals. It may be doubted, however, whether this 

 alone justifies the use of the term, and whether there is not another 



1). Haswell— On the Excretory System of Temnocephala. Zool. Anz., XV. Jahrg., 1892. p. 

 149-151. 



2). Lang— Die Polycladen cles Golie^ von Neapel. p. 165-166. , This writer also applies the 

 term "intracellular" to the vas efferens of some polyclads. 



