14 RALFS, ON DIATOMACE. 
thickest part with a single cylindrical nucleus imbedded in 
its substance. 
Professor Kélliker’s account of the tissue bemg thus com- 
pletely confirmed in these two instances, and the description 
here given of its appearance in the arteries of the frog’s foot 
being an independent confirmation of the general doctrine, 
there seems no reason any longer to doubt its truth. 
It further appears, that in the pig’s intestine the muscular 
elements are, on the one hand, capable of an extraordinary 
degree of extension, and, on the other hand, are endowed 
with a marvellous faculty of contraction, by which they may 
be reduced from the condition of very long fibres to that of 
almost globular masses. In the extended state they have a 
soft, delicate, and usually homogeneous aspect, which becomes 
altered during contraction by the supervention of highly 
refractmg transverse ribs, which grow thicker and more 
approximated as the process advances. Meanwhile, the “ rod- 
shaped” nucleus appears to be pinched up by the contract- 
ing fibre till it assumes a slightly oval form, with the longer 
diameter transversely placed. 
I will only further remark, that these properties of the 
constituent elements of involuntary muscular fibre explain, in 
a very beautiful manner, the extraordinary range of contrac- 
tility which characterises the hollow viscera. 
Nores on the S1uicrous Cety of Diatomacem. 
By J. Rarrs, Esq. 
Tur few remarks now offered to the British Association, 
“upon the siliceous cell formed within the frustules of 
several Diatomaceze,” have been written rather to stimulate 
the researches of my fellow-students, and to elicit their 
opinions, than to communicate any new facts. 
I believe that in my description of Fragilaria (Himan- 
tidium) pectinalis, in 1843, I was the first to indicate the 
occurrence of these cells, in the following words: “ Within 
the frustule there is apparently another siliceous frustule, the 
lateral margins of which are rounded, having striz like the 
outer frustule. In the longer frustules it is nearly elliptic, 
but in the shorter ones appears as if truncated at the ends, 
and in both it occupies the whole interior of the frustule, 
except the corners where the puncta at the ends are situated ; 
