100 Macueay Memoriat Vouvume. 
in the living animal as a clear layer superficial to the epidermis; it varies considerably 
in thickness in the different species: the thickness is greatest—'004mm. in 7. fasciata; 
in Z. comes, T. Dendyt and 7. Nove-zealandi@ it is nearly as great ; in 7. mznor it is 
much more delicate and considerably thinner than the epidermis, the thickness of the 
entire integument (including cuticle, epidermis and basement membrane) in this 
species being only ‘006 to ‘008mm. In 7. /eringzz it is still thinner—-003mm. In 
all the species it and the other layers are much thinner on the tentacles and the 
suckers than elsewhere. It is of homogeneous character, but perforated by the 
openings of numerous pore-canals continuous with those of the underlying layers. 
Its surface, in the case of 7. fasceata and 7. comes, is thrown into numerous regular 
minute ruge, which, however, are probably not present when the animal is fully 
extended. In sections of specimens that have been well fixed and hardened its outer 
surface appears, in the case of some species, to be covered with minute blunt papille 
(PI. x. fig. 6), between the bases of which are the apertures of the pore-canals; these 
papillze do not occur in all the species; I have observed them in the case of 7. 
fasciata, T. comes and 7. Nove-zealandie ; they are absent in 7. minor and T. 
Dendy. 
Below the cuticle is a distinct nucleated protoplasmic layer or epidermis (PI. x. 
figs. 1-8, ef. and PI. xiv. fig. 4, e.). Weber describes this as a layer of cells of 
cubical form, but varying somewhat in shape with the state of contraction or 
extension of the part, with indistinct, or altogether without, cell-outlines.* I have 
never been able to see any trace of cell-outlines, though I have examined preparations 
treated by every method likely to be favourable to their detection if present 
(impregnation with nitrate of silver among the number); and I therefore prefer to 
adhere to the view that, though this epidermal layer is developed from a layer of 
rounded cells, yet in the adult condition we have to do with a complete syncytium, 
and not with a layer of cells as such.t 
In all the species examined this epidermal layer is striated in a vertical or slightly 
oblique direction. Many of the lines or striz are produced by the pore-canals, the 
openings of which are to be observed on the surface of the cuticle ; but they seem to 
be too numerous to be all capable of being accounted for in this way; and there is 
some sort of vertical fibrillation of the protoplasm as well, due apparently to the 
presence of closely-set slender columns similar to those described by Béhmig as 
occurring in the epidermal cells of Rhabdocceles. This marking is particularly 
distinct in 7. guadricornis (see Pl. xiv. fig. 4). In many sections the pore-canals are 
distinctly to be seen as vertical channels running through the epidermis, sometimes 
very narrow, sometimes comparatively wide. In tangential sections (Pl. x. fig. 4) it 
* Weber, /.c. p. 5. 
+ Braun (/.c. p. 422) comes to the same conclusion as regards the absence of cell-outlines. 
