260 EMMERICH ON THE MORPHOLOGY, CLASSIFICATION 
which indeed for the greater part are reduced almost to the mere 
and most necessary organs of existence, those of nutrition and 
of reproduction, the conviction must at once urge itself upon 
our mind, that there can be no affinity between them and these 
parasites. We observe no degeneration in them in any other 
respect; excepting the eye, they have as perfect a normal deve- 
lopment in all other respects as the species furnished with the 
largest facetted eyes. Many indeed possessed the capacity of 
doubling themselves up, a power which is as much opposed to 
the principles of a parasitical life as anything that can be con- 
ceived. The existence of spine-like appendages in many of the 
species of Ampyx at the angles of the cephalic shield, and even 
at the forehead, can likewise not be reconciled with such an 
assumption. Cryptolithus, although not contractile, seems from 
its form to have been equally as little intended by nature for such 
a mode of life. Everything indeed suggests to us the necessity of 
seeking still further for eyes even in these species, and no slight 
hope of success is held out to us by the fact of Phacops crypto- 
phthalmus possessing eyes, although such small ones and situated 
so nearly on a level with the cheeks, that they can only be detected 
in the fossil by a practised eye. The fact of blindness is there- 
fore at all events limited to the last-named genera, Cryptolithus, 
Ampyx and Arges, and even with regard to them forms but a 
very doubtful characteristic; all the other genera possessed eyes 
during their lifetime. Some, for instance Phacops and Phil- 
lipsia, possessed a horny membrane furnished with large facets 
that were even visible to the naked eye; in others, and that in 
the majority of Trilobites, the eyes were smooth, not facetted 
externally: and there finally remains a certain number respect- 
ing the eyes of which we know nothing, since they were destroyed. 
To these latter with “ oculi hiantes”’ belong the greater portion 
of the Trilobites which were formerly considered as blind, to- 
gether with the true Calymene and Homalonoti. 
The cephalic shield presents various other important charac- 
teristics besides the difference of the eyes, but which have not 
been taken notice of in drawing up the generic characters. Of 
these I consider the facial suture as the most important. I have 
already alluded to the cephalic shield as being composed of se- 
veral pieces connected by sutures. This is a peculiarity of this 
family, not possessed, to my knowledge, by any other of the 
crustaceous animals ; it will therefore scarcely be surprising to 
