254 EMMERICH ON THE MORPHOLOGY, CLASSIFICATION 
cluded from it in all the Trilobites, and constitute a free ap- 
pendage, generally capable of a more or less independent move- 
ment. The cavity of the body, which contained the intestines 
of the animal, was only formed by the dorsal parts of the rings 
(terga), and by the abdominal parts opposite to them. The terga 
only have been preserved of these two different parts, owing to 
their having been of a calcareous nature in the living animals 
(Professor Hiinefeld has found a considerable quantity of phos- 
phate of lime, in addition to the carbonate of lime, in pieces of : 
the shell) ; the abdominal portions were of a membranous nature, 
and decay has therefore destroyed them, together with the 
branchial feet, which were probably peculiar to these animals. 
Thus every ring consisted essentially of six elements. The 
structure of the rings of the tail entirely corresponds with this, — 
with the exception that the free motion of the fins ceases simul- 
taneously with the loss of the moveability of the joints of the 
axis, and that the former cohere immoveably among themselves 
and with the axis. The abdominal pieces were likewise of a 
membranous nature, and have therefore disappeared. The ele- 
ments of the rings, by the junction of which the cephalic shield 
is formed, can also be demonsirated in the latter, in the same 
number and position as in the rings of the thorax; they bear 
the same relation to the latter as the elements of the dorsal ver- 
tebrae of Mammalia to those of the three vertebre of the head; 
they are horizontally extended, and not united with one another 
by articulations but by sutures. These sutures remain di- 
stinctly visible in the Trilobites, forming a characteristic feature 
of the family. One of these sutures is very well known under 
the name of facial suture: for a long time it could not be ex- 
plained by geologists, and has frequently given rise to strange 
interpretations (Pander), but much of its enigmatical character 
disappears on more accurate observation. These sutures, in my 
opinion, form an important objection against the ingenious hy-~ 
pothesis of Burmeister, who considers the Battus to be the most 
imperfect or undeveloped state of the Trilobites. Battus exhibits 
no traces of facial sutures. This assumption however is in op- 
position to a general law of nature, namely, that parts which 
were separated in the early state of an animal (for instance, the 
parts of the subsequently monopetalous flower, parts of the 
skeleton, as the pelvis, temple bone, &c.) may subsequently 
unite into one whole, but on the contrary a previously develope 
