STUDIES OX THE ECTOPAllASITIC TREMATODES OF JAPAX. 7 



opiinon has been advanced liy Brandes,'^ and as the genesis of the 

 membrane in question lia.s not been made out embryologically, I have 

 thought it better to nse a non-committal term, and have adopted for 

 this ])urpose the name used by AVright and Macallum,"^ although 

 it is in some respects not a very convenient one. 



Three layers can be distinguished in the investing membrane of 

 the ectoparasitic Trematodes. These I shall call the cuticle, the siih- 

 cuftclc, and the basement memhmnc. These terms, I am well aware, are 

 all preoccupied, and bear different significations according to different 

 writers ; but the coinage of new words is not very desirable and is 

 moreover not an easy task for one writing in a foreign language. 

 Words hitherto in use can, however, be used in a new sense without 

 any danger of occasioning confusion, when clear definitions are given. 

 The term " subcuticle" might be somewhat objectionable, as liable 

 to be confounded with the " Subcuticularschicht " of Taschenberg 

 and some other writers on Trematodes ; but this is now so o-enerallv 

 recognised to be nothing more than the cortical portion of the 

 mesenchvma that there is, I believe, no serious dancfer of in- 

 troducing confusion of ideas by adopting, in this paper at least, the 

 terminology here proposed,"-' in place of ' epidermal layer ' which I 

 used in my former pjiper. 



The cuticle is a very thin, structureless, refractive layer which is 

 very distinct in fresh specimens. In sections its existence is indicated 



1). Brandes — Zum feineren Bau der Trematoden. Zeitschr. f. wiss. Zool., Bd. 53, 1892, p. 

 558. 



2). Wright and Macallnm — Sphyranura Osleri. Journal of Morphologj', vol. I, 1887. p. 1. 



3). Monticelli in a paper which was received after the above had been written, calls the 

 investing membrane " ectoderma," and claims to have demonstrated in it the remnants of the 

 original nuclei in the form of vesicles containing deeply stained corpuscles. Granting that the 

 nuclei of the original epidermis may in some species remain in a comparatively unaltered state, 

 it seems to me that the vesicles figured by Monticelli are too numerous to be regarded as the 

 remnants of the nuclei of the ectoderm of the Cercaria, which are, according to the statements 



