MOLLUSKS 165 
The male Argonaut is only about one-tenth as large as the 
female, being about one inch in length. Previous to the breeding 
season the third arm on the left side is seen to be developing inside 
ofasac. Later this sac splits along on one side and turns inside out, 
thus freeing the arm, which is then seen to be more than twice as 
long as the ordinary arms of the animal, and to terminate in a long 
pointed filament which was itself developed in a sack very much as 
was the base of the arm. <A numberof long filamentous tubes con- 
taining spermatozoa are placed within the cavity of the sac at the 
base of the arm. At the breeding time the entire arm is cast off, 
enters the mantle cavity of the female, and adheres to her body. 
The male Argonaut never develops a shell. 
It is in the contemplation of creatures such as this that we 
come to realize the hopelessness of any attempt to measure by our 
puny standards the immensity of time that has elapsed since evo- 
lution began to mold the manifold forms of life. How long may it 
have been before such a remarkable contrivance as the shell-like 
brood-pouch and such a curiously modified arm as that of the male 
Argonaut could have been developed? 
Altogether there is no more comprehensive picture of the 
course of evolution than that furnished by the fossil shells of 
Cephalopods. We see the straight-shelled Nautilus race that 
swarmed in the ancient Silurian seas, when the whole western half 
of New York State was submerged by an ocean continuous with 
what is now the Pacific. Afterwards in Devonian times we find the 
sculptured Ammonites appearing in a vast variety of forms. Then 
the Nautilus race slowly faded away until to-day we find its last 
lingering descendant living in the depths of the Pacific, while the 
Ammonites, their shells coiling and uncoiling in writhing, snake- 
like shapes, died out forever, while the Chalk cliffs of England were 
yet beneath the sea. 
Only the soft bodied squids and octopi which first appear in 
Triassic seas, still survive in reduced numbers in the oceans of 
to-day. 
