8o 



THE CHAIN OF LIFE. 



the worms. But still the two types, that of the Mollusk and 

 the Articulate, are distinct even from their first appearance in 

 the egg, nor have either any close affinities with the Protozoa, 

 the Hydroids, or the Corals. 



Both types meet us in the Early Cambrian, but while the 

 Mollusk is there represented only by low forms, the Articulate 

 is then not only in the humble guise of the worm, but in the 

 complex and highly organised form of the Trilobite (Figs. 28 

 and 75). What older phases they may have passed through we 



Fig. 76.-Transverse section of Calymene. A Silurian Trilobite. -After Wolcott. 



a Dorsal shell, b. Visceral cavity, c, Legs d, Epipodite-giU-cleaner or palp. 

 ' e. Spiral gills. 



know not ; but in the Lower Cambrian we have various forms 

 of these animals, including some of the largest known as well 

 as some of the smallest ; some of the most complex in num- 

 ber of parts as well as some of the simplest. These animals, 

 in short, seem to have appeared at once all over the world 

 fully formed, and in a variety of generic and specific forms ; and 

 nothing short of a very large faith in the imperfection of the 

 geological record can suffice to account for their evolution. 

 A Trilobite is a creature in whose structure the number three 



