THE FRONT OF THE PROCESSION OF LIFE. 81 



a Land magnifier ? If not, the beautiful and perfect struc- 

 ture which it displays will compensate for the trouble of 

 procuring the means to make the observation. Some scores 

 of little lenses, arranged with the most perfect symmetry, 

 each set in its little telescopic tube, form upon the retina 

 of the little insect the various portions of an image of some 

 external object. Such eyes had the trilobite (Fig. 28). It 

 is marvelous that such delicate structures have been so 



Fig. 28. The eye of a Trilobite magnified. 



a. Eye of Asaphus caudatus. b. A few facets of the eye ofCalymene 



macrophthalmus. 



perfectly preserved as in some trilobites which I have ex- 

 amined from the neighborhood of Dubuque, Iowa. These, 

 however, existed in the period following the Potsdam. The 

 trilobite was tri-lobed in two respects. Longitudinally, the 

 oval form was divided into head, body, and tail ; while in 

 the other direction a couple of lengthwise grooves divided 

 the animal into middle, right, and left lobes, or regions. 



In this earliest scene of animalization, mollusks and ra- 

 diates play comparatively an inconspicuous role. But it 

 must be remarked that both these types of existence had 

 been introduced. Among the molluscs we have found, be- 

 sides the representatives of Brachiopods already mentioned, 

 a few other members of the same class, and also some coiled 

 univalves, which belong to the higher class of Gasteropods. 

 Among the radiates we have in the Old World a few rep- 

 resentatives from the middle of the sub-kingdom in point 

 of rank, while among Protozoa we find a few forms relatec 1 



