STUDIES ON THE ECTOPARASITIC TREMATODES OF JAPAN. J I 



prodnced by ii distinct external e|)ltheliuin such ns has been described 

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

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

 cells whose internal part lias 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 HaswelT^ has extended the application 

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

 ceplmla, 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 intracellular 

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

 who used the term for the first time — ; and to avoid any misinter- 

 pretation I shall quote his own w^ords. He says,^^ "In ziemlich 

 o-rossen Abständen verdickt sich die Wand der grossen Canäle 

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

 dickten Stellen inserirt sich stets je ein Büschel viel längerer Cilien. 

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

 Strecke je eine einzige Zelle die Wand der grossen Canäle bildet ; mit 

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

 bohrte Zellen dar." From this it is T 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 In' 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. 

 14C-151. 



2). Lang — Die Polycladen des Golfes von Neapel, p. 1G5-16G. This writer also applies the 

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



