Palcontological Speculations. — Gratacap. 219 
further reinforced the numerical results. It was a time when 
as at the Philippine Islands today, true periodicity had dis- 
appeared, and eggs, larvae, and propagating individuals may 
have been found at all times. 
The remaining fa^^tors that might have influenced the 
successful development of trilobites in the Cambrian seas 
were water motion, currents, land movements, and living sur- 
roundings. 
The prevalence of high waves, the rushing in and out of 
heavy volumes of water, would have been extremely detri- 
mental to the lives and propagation of crustacean animals if 
they were exposed to its mechanical violence and its accom- 
paniment of moving stones etc. But the evidence points to 
the occupancy of shallow shores or basins by the Cambrian 
trilobites and those generally of a sandy or muddy nature, 
in which no disturbances inimical to their quiet and contin- 
uous existence appeared. The conditions of a slowly advan- 
cing or receding sea (vide Chamberlain, Jour, of Geol., Vol. 
VI, p. 449) permitted their enormous multiplication along 
the thermally benign coast areas, while the absence of rapid 
or destructive currents seems certain from the usually con- 
formable and exact lamination of the beds where the trilo- 
bites occur in large numbers. 
Finally their living surroundings were almost invariably 
favorable, food was abundant and enemies absent. Their 
specific and generic variations are not so easily explained. 
They certainly point to an inheritance of characters developed 
far back of the Cambrian day, characters alsO' quite deeply 
established, and ineffaceable by interbreeding or pan-mixia. 
The Cambrian faunal trilobite expression is that of a broad 
anterior shield more or less genally extended, a conoid head, 
an extended series of pleural segments, and a reduced or absent 
pygidium. Their separation into species and even genera sug- 
gest inherited anomalies in their evolution from the annelid 
(Bernard), and even point to divergent origins from differing 
annelid types. Bernard (Quar. Jour. Geol. Soc, Vol. 50) has 
described trilobites "as fixed specialized stages in the evolution 
of the Crustacea from an annelidan ancestor, which bent its 
mouth round ventrally so as to use its parapodia as jaws." Now 
it seems inconceivable that if evolution brought about this 
