Life-history and Anatomy of the Appendieulate Dlstomes. 3G1 



to form the cuticula when the epithelium was finally sloughed off. As 

 in the case in hand, the epithelium has been interpreted to be the 

 cercariau epithelial covering which has, for some reason, been retained 

 beyond the cercarian period. Heckert (1889) and Looss (see Braun, 

 1893, p. 818 note, 819) have observed two distinct layers of epithelial 

 cells in the external covering of the Cercaria (in some cases also of 

 the Redia) which where shed one after the other, usually during the 

 cercarian period, but in some cases not until after the end of this 

 period when the young worm had arrived in its final host. Looss 

 (1. c. p. 63) records that "Bei der Cercaria macrocera, ehe sie ihre 

 völlige Reife erreicht hat, sieht man die Körperbedeckung sehr deutlich 

 aus einer zelligeu Membran bestehen, welche sich auf die des Schwanzes 

 fortsetzt. Ebenso deutlich erkennt man aber unter dieser Haut bereits 

 die spätere Cuticula." Kerbert (1. c.) observed external epithelial 

 cells in the adult Distomum wesfermanni. Minot (1877, p, 456) re- 

 ports the following observation on certain Cestodes: "Ich habe aber 

 an Taenia, Bothriocephalus und Caryophyllaeus eine Schicht, in 

 welcher ich einige Male deuthche Cylinderzellen gefunden habe, ausser- 

 halb der sogenannten Cuticula, entdeckt. Die Zellenschicht war die 

 wahre Epidermis, auf ihr liegt eine äusserst dünne Cuticula, und die 

 angebliche faserige Cuticula auct. ist die Basilarmembran." 



That the observations above recorded on the youthful Äpoblema 

 appendiculatum have an important bearing on the much mooted ques- 

 tion of the origin and morphological significance of the cuticula of 

 Trematodes and Cestodes is obvious, and they would seem to support 

 the position of the earlier investigators Schneider (1873), Minot (1877, 

 1878) and Kerbert (1881). These authors hold that the integument- 

 ary membrane of Trematodes and Cestodes is not a cuticula, in 

 proprio sensu, in that it is not a membrane which is secreted by an 

 epithelium, but is a basement-membrane, which is exposed and 

 becomes the outer body-covering when the integumentary epithelium, 

 characteristic of the earlier developmental stages of these worms, is 

 cast off. 



I would not range myself on the side of these authors, however, 

 and call the "cuticula" of Trematodes a typical basement - membrane, 

 not even the cuticula of the appendix of the worm under discussion, 

 in which an epithelium appears on the outside of it. A basement- 

 membrane is a structure the genesis of which is not known. We do 

 not know in most cases whether it is to be reckoned an epithelial 

 structure, the product of the epithelium it supports, a connective tissue 



Zool. Jahrb. XI. Abth. f. Moiiih. Oj. 



