72 



s. GOTO. 



way of interpretation. Pintner'^ has described a well developed 

 epithelium on the main vessels of the excretory system. PTence I 

 think it is more in accordance with the procedure elsewhere general, 

 to reo-ard the excretory vessels not as intracellular but as bounded by 

 a true epithelium, which however, consists of only a small number of 

 cells, so that the single cells have been greatly flattened and have 

 assumed the form of a tube by the union of its opposite margins. In 

 this case, the cavity of the vessel would be as truly outside the cell as 

 any other intercellular spaces. It is true indeed, that according to 

 Schwarze-' the terminal excretory vessels of the distomes are formed 

 by the absorption of the axial part of an originally solid string of cells. 

 But even taking this statement as it stands — and without suspecting 

 whether it mav not be formed by a simple rearrangement of the cells as 

 is stated by Looss^^ to be the case in the genital ducts, — it is not neces- 

 sary to su])pose that exactly the same process takes place in the smaller 

 vessels as in the terminal vesicle ; .and therefore the view is perfectly 

 allowable that where the cells are arranged only in a single row, each 

 one assumes, to speak on supposition, a crescent shape at -first and 

 then closes into a tube l)y the union of the opposite margins. Such 

 tubes, open and placed end to end would form a vessel such as is 

 found in the turbellarians. There is another objection to the word 

 "intracellular"; and that is the presence of cilia on the internal 

 surface of the wall of the vessels. So far as our experience goes, there 

 is no case in which cilia are found growing ivitliin the cells, but only 

 on the external surf ice. 



1). Pintner — Untersuch, ü. d. Bau des Bandwurmkörpers. Wiener Arbeiten. Bd. 3, 1880. 

 p. 21. 



2). Schwarze— Die postembryon. Entwickl. der Trematoden. Zeitschr. f. wiss. Zool. Bd. 

 42, 188G. p. 58. 



3). Looss— Ist der Laurer'sche Kanal der Trematoden eine Vagina? CcntralM. f. 

 B.akteriol. u. Parasitenk. Bd. XIII, 1893. p. 809 (Xr. 25). 



