200 BULLETIN OF THE 
imprints as though it had contracted or shrunk after the decomposition 
of the muscles forming the leg. 
That such a delicate membrane as enclosed the appendages and 
ventral surface of the Trilobite may be preserved so as to be observed 
in the fossil state, there is little doubt. It may be an impression in 
fine, smooth shale, or by the replacement of the parts by a mineral 
differing in color from the matrix, so as to show them distinctly. In 
Eocene fresh-water strata on the Isle of Wight the gill feet of Branchi- 
pus have been found. They were in a fine argillaceo-calcareous rock 
and stained with iron so as to show as well as in a photograph.* It 
is difficult to conceive of a more delicate test of the preservation of 
the branchiæ, and other parts liable to destruction from their nature, 
than this. 
The Intestinal Canal. — Attention was first called to the existence 
of the intestinal canal in the Trilobite by Prof. Beyrich, who discovered 
it in a specimen of Trinucleus ornatus. M. Barrande subsequently 
gave numerous illustrations of its preservation in Trinucleus Goldfussi, 
where, he says, it extended from the middle of the glabella along the 
interior of the median lobe to the extremity of the pygidium. In some 
examples it is filled with very fine, soft clay. This substance has, per- 
haps, largely contributed to preserve the form of the canal, which, once 
filled and buried in incompressible sand, has undergone no other de- 
formation. There must have been some peculiarity of conformation 
that preserved the intestinal canal in this species, as in other Trilobites 
from the same quartzites no traces of it are to be seen.f M. Barrande 
mentions that Dr. A. de Volborth discovered in an Zlleenus a length- 
ened and articulate organ which originated in the glabella and became 
attenuated towards the pygidium.$ A cast of the interior, as shown 
in Plate IV. fig. 7, might have such an appearance. This, however, 
is conjectural, as I have not seen an illustration of Dr. Volborth's 
Specimen. 
In cutting sections of Trilobites it was a very rare occurence to find 
traces of the intestinal canal. One specimen out of one hundred was a 
large proportion. The visceral cavity was usually filled with calespar, 
and all vestiges of the canal or any other organ obliterated. 
In a note taken while cutting sections in December, 1876, it is 
stated that when grinding down a section from the anterior towards 
* Nature, p. 381, 1877. 
+ Ueb. Trilob., IT. Stück., p. 30, Plate IV. fig. 1, c, 1846. 
t Sys. Sil. Boh., I. p. 229, 1852. $ Ibid., II. p. 182, 1872. 
