86 THE NORTHERN MICROSCOPIST. 

=_ 
the shell or valves, which being siliceous, are more likely to be 
preserved as fossils, particularly where the matrix has been of a 
finely levigated character. Where the sediment has been arenace. 
ous, such as the Downton sandstone, we rely then mostly upon 
casts such as from which the C. beyrichia have been worked. 
When the imbedding substance is an argillo-calcareous, the valves 
are tolerably accurately preserved, and are easy to make out, 
Our short and necessarily imperfect sketch of this little Crus- 
tacean is at an end, yet we cannot close without being struck with 
the remarkable fact of the persistency with which the Cypris family 
has held its own through all the ever-varying changes of climate, of 
temperature, and of time. ‘That from the earliest periods, whilst 
ancient continents were being ground down, and new ones built 
out of the degraded matter ; that whilst land has changed places 
with the sea, and the sea has possessed the land areas ; throughout 
all the vicissitudes of the moisture-laden atmosphere of the Car- 
boniferous period, the semi-tropical climate of the Tertiary, and 
the Arctic condition of the Pleistocene, throughout all these, and 
more changes than we can enumerate, has this apparantly insignifi- 
cant form held its own. 
More particularly are we struck with the fact when we reflect 
upon all the huge forms, such as the Mastodon, and some of the 
Elephants, of the Tertiaries, the Pleisosaurs and Ichthyosaurs of 
the secondary periods, and the Labrinthodon and the Devonian 
fishes of the Palzeozoic which have all had to succumb to the various 
changes of the past, and have either been exterminated from our 
land or become totally extinct. Yet, here we have that which 
some of these extinct creatures may have sucked up into their 
huge jaws, and swallowed by the thousand, still existing in forms 
little modified since its earliest advent. 
Finally, to what does this apparent persistency of type point? 
Is it persistency of type? If so, then where does the great 
doctrine of Evolution step in to this particular form? If it is of 
persistency of type, then how can we account for its repeated 
appearance, through the geological range of the stratified rocks, 
other than by special creations ? 
That it is persistency of type, and not special creations we 
believe, and believing that, we say that this is one of the many 
instances of persistency which go to say that Evolution is not yet 
universally made out. 

