514 WILLIAM BATESON. 
fusiform cells are generally most abundant at that level of the 
skin at which the nuclei of the long cells are placed, the 
appearance is suggested that they form a second layer of ecto- 
derm cells ; but for the reasons above stated it seems likely that 
this is erroneous, and that there is no such definite second layer. 
The resemblance between this skin and that of some 
Nemertines, e.g. Monopora vivipara (Salensky, ‘ Arch de 
Biologie,’ 1884), is very close. In this animal the same 
spongy appearance is produced, and it is possible that the 
deeper layer of ectoderm may be capable of the same expla- 
nation. 
The skin of B. Kowalevskii differs in some ways from 
that of B. minutus, &c., especially that of the trunk, in which 
the large goblet cells are comparatively rare. In all parts of 
the skin round, unicellular glands are more or less frequent, but 
their contents stain more or less deeply with hematoxylin, &c. 
These cells often fall out, leaving empty spaces. In the collar 
of B. Kowalevskii the skin is very thick and is full of very 
long cells (figs. 80 and 81) containing granular contents, which 
stain very deeply. 
Fig. 79 shows a section of part of the proboscis skin in 
which the layer of nerve-fibre is very thick. In the upper 
part of this kind of skin there is a definite row of long nuclei 
which with some reagents assume a dice-box shape, probably 
due to preservation. To what extent these cells reach the 
whole depth of the skin cannot be affirmed, but many of them 
can be traced into fibres which run into the layer of nerve- 
fibre. 
Nervous Concentrations in the Skin.—As has been 
already mentioned, in all the parts of the skin a greater or 
less quantity of unstained substance may be found in the base 
of the skin. The substance contains no nuclei (excepting a 
few in the nerve-sheath of the base of the proboscis), and may 
be seen, especially in fresh osmic acid preparations, to consist 
of fine fibres. Into it run the tails of ectoderm cells. In the 
next place fibres may frequently be seen running out of it 
through the basement membrane, and losing themselves 
