DESMIDS AND DIATOMS. 587 
the shrill clarion voice of the Downy Woodpecker, you 
hear a noise like a falling stone through the branches of 
the tree; it is the shrike: he has struck his victim, and 
if he does not devour it upon the spot, it is hung on the 
crotch of a limb to serve as a meal at some future time. 
DESMIDS AND DIATOMS. 
No. I. 
THEIR GROWTH AND GEOLOGICAL IMPORTANCE. 
BY PROF. L. W. BAILEY. 
[Concluded from page 517.] 
In descending from the study of the higher to that of 
the lower forms of life, nothing is more remarkable than 
the manifold and often varied means by which that life 
_ is multiplied and perpetuated. In all four departments 
of the Animal Kingdom this is found to be the case, the 
higher groups in each producing for the most part a lim- 
ited number of offspring, which, however, they nurse with 
proportionate care, while, as we pass to those occupying 
a lower grade, Nature seems to guard against the extinc- 
tion of a species by vastly augmenting the reproductive 
power of the individual. So strikingly is this the case, 
that fishes, worms, the moss-like mollusca and the polyps, 
the lower groups under their several types, have been 
well styled the Embryonic or Reproductive Classes. Nor 
is this observation true only within the limits of a single 
department. It is equally the case when one of these 
classes is compared with another, the difference, however, 
now appearing not so much in an inequality in the number 
of actual offspring, as in the introduction of new modes of 
