THE GEELONG NATURALIST.. Gl 
upper. Professor Ramsay says "that where we have: a complete: 
succession of rocks the species die out and appear gradually and 
almost imperceptibly; that where there is any sudden change in 
the fauna, it is always accompanied by an unconformity in the- 
rocks. .À break in the current of animal life is believed to be 
always accompanied by a break in the succession of rocks, and the 
greater the difference of forms between the upper and the lower- 
rock the greater the interval of time between their successive 
deposition. 
Let us glance back to the time when the different families of 
mollusca first started their career in the race for life. The Spirula, 
one of the cuttlefish tribe (cephalopoda) having an internal shell,. 
appears to be the last of that immense tribe that once swarmed in 
the ancient seas. According to Mr Grey, of the British pfuseum, 
there is reason to believe that the Spirula is the nearest approach to. 
the Ammonites. i 
This animal had all the general external characteristics of the- 
Cuttlefish ; it had a large and distinct head, with eyes on each side, 
two long arms with elongated peduncles and a bag-like mantle, with: 
a process in the middle above, and one on each side of the anal tube. 
below. But it differs from the Cuttlefish in being destitute of fins. 
Being rather compressed behind the mantle is free from the body 
on all sides of its anal edge, and the funnel is free from the: 
mantle. 
Mr Grey thinks the Ammonites, from the texture and the 
small size of the last chamber were internal shells, like the Spirula; 
the principal difference being in the siphon being always on the 
dorsal margin of the whorl, and the septa being foliated on the 
edge. We may consider the Spirula as one of the life links from 
the old Cambrian days. 
Perhaps few subjects are fraught with more interest to the: 
scientific world than the above with its high antiquity and peculiar 
form, for in simplicity of structure and permanence of principle, it 
is practically the same to-day as it was untold ages ago, when its: 
order—with its twin sister in age, the Brachiopod—first began. 
This fact does not appear to offer a great deal of support for- 
the theory of the Origin of Species. Here is a molluse born into. 
the world in the old, or rather the young, Cambrian and Silurian 
days, sweeping with little variation through the sea of time; exhibit-- 
ing a wondrous tenacity of life amidst violent changes and strange 
conditions, and sending off from the parent species sub-orders in: 
immense numbers. 
