be differently constituted from that of Neomenia carinata where a 
single layer of short spiculae is superficially imbedded in the outer 
layers of the skin, and where the implantation of these spieulae is 
such as to leave the pointed ends of the spines protruding between 
more or less numerous warts or glands in the skin. A prolonged 
boiling of a portion of the skin of Proneomenia with caustic potash pro- 
ved that no separate spines were thereby set free , but that the spiculae 
were kept together in a way differing from that which obtains in Neo- 
menia carinata. The presence of such spiculae could however be easily 
demonstrated with weak powers, the outer surface of the skin then 
showing the appearance of fig. 6. Transverse sections moreover 
show that the layer of spiculae is not single but multiple (fig. 23), 
whilst chemical analysis proved the spicules to consist essen- 
tially of carbonate of lime. 
The study of thin sections stained with pierocarmine gave the 
following results concerning the histological constitution. 
Exteriorly applied to the layer of circular muscles, which all 
over the body is situated immediately under the integument, we 
find a layer of cells with distinct nuclei. This layer is generally 
only one or a few cells thick, it stains more conspicuously than 
either of the adjacent tissues, muscular as well as integumentary 
and must no doubt be regarded as the matrix for the latter tissue. 
So the integument consists of this matrix (with its radial prolon- 
gations to be mentioned hereafter), of the spicules and of the in- 
terspicular substance, by which the spicules are held together. 
This interspicular substance is wholly homogenous and structure- 
less and is uniformly light rose-coloured after treatment with pi- 
crocarmine. In it the calcareous spicules are imbedded and very 
thickly set: after decalcification the interspieular substance remains 
unchanged and empty spaces, which entirely preserve the original 
shape of the spicules permit us to study the growth and attach- 
ment of the latter in microscopical sections. On account of the 
behaviour of the interspicular substance towards acids and towards 
eaustic potash, by both of which it is not visibly influenced, Iam 
“ inclined to regard it as a chitin-like substance, a sort of chitinous 
