tise, Raed Baa 
348 Canadian Record of Science. 
in the application of the discoveries in the embryology of 
recent animals to the interpretation of the primitive forms 
of the Cambrian seas), he takes the trilobites as the most 
interesting forms, viewed from the stand point of evolution, 
as being organisms of the highest type (for that age), be- 
cause in them the results of evolution are most manifest. 
After speaking of the trilobites as Arthropods with a 
chitinous test, living in the water, breathing by gills, fur- 
nished with numerous pairs of thoracic limbs of which some 
are connected with the jaws and some with the abdomen, 
he proceeds to give in outline a description of the parts of 
their bodies and their use in the economy of the creature. 
The metamorphosis of the Cambrian trilobites has been 
shown by Barrande for the genus Sao and by Matthew for 
the genera Liostracus Ptychoparia and Solenopleura. The 
three latter exhibit similar series of metamorphosis and 
so are naturally grouped in the same family. On the other 
hand the changes in the young of Paradoxides follow an 
independent line of development, showing that this genus 
belongs to a different family. ‘ We see then that in the 
trilobites of the fauna called Primordeal there were already 
differences in the mode of development; and these differ- 
ences in the forms of the same group living at the same 
epoch, correspond certainly to a grade of evolution which 
is not the same; this compels us to admit that before the 
time when this trilobite fauna lived, there must have been 
another from which it proceeded.” 
Another argument used by Dr. Bergeron is that the 
size of the front lobe of the glabella in embryonic forms of 
the early trilobites foreshadowed the genera Paradoxides 
and Olenellus, which are similarly characterized in the 
adult stage. However, he thinks that more weight is to be 
given to the small size of the pygidium in these and other 
primordeal genera as indicating the primitive aspect of the 
Cambrian trilobites, for in the embryonic trilobite the pygi- 
dium is small compared with the cephalic shield. 
The development of the genus Agnostus also is taken as 
showing the line of change through which the genera of 
