INVERTEBRATE ANIMALS; 
IN VERT EB RAT A. 
E now come to the second great division into which all animated beings have been 
distinguished. All the creatures which we have hitherto examined, however 
different in form they may be, the ape and the eel being good examples of this 
external dissimilarity, yet agree in one point, namely, that they possess a spinal 
cord, protected by vertebrae, and are therefore termed Vertebrated animals. 
But with the fishes ends the division of vertebrates, and we now enter upon 
another vast division in which there is no true brain and no vertebrae. These 
creatures are classed together under the name of In vertebrated animals ; a somewhat insuffi- 
cient title, as it is based upon a negative and not on a positive principle. Whatever may 
be its defects, it has been too long received, and is too generally accepted to be disturbed by a 
new phraseology, and though it be founded on the absence and not the presence of certain 
structures, it is concise and intelligible. 
Numerous as are the species of the vertebrated animals, those of the invertebrates out- 
number them as an army outnumbers a company. Although many species of mammals, birds, 
reptiles, and fishes, are at present known to science, and the yet unrecognized species are 
necessarily extremely numerous, there is some hope of obtaining an approximate calculation of 
their respective numbers. But with the invertebrates, any approach to a census even of known 
forms is well-nigh impracticable ; and as it is evident that the ocean alone contains within its 
fathomless depths myriads of beings as yet hidden from mortal eyes, the reader may conceive 
the utter impossibility of offering the slightest conjecture respecting their numbers. 
SOME EARLY REMINISCENCES BY THE AMERICAN EDITOR. 
The study of invertebrate forms in America is of so recent an occurrence that there are 
a number now living who remember that, with the exception of the mollusks or “shell- 
fish,” forty years since the student had but the merest fragment of recorded knowledge 
to aid him. 
At that time the four great classes of Cuvier were recognized as the legitimate foundations 
of classification : the two great primary divisions being Vertebrata and Invertebrata — those 
having an internal bony skeleton, and those having none. At this time, even in the immediate 
vicinity of the Massachusetts metropolis, he was a wise person, beyond the “general,” that 
had a definite idea of the nature of the very few actinias then known on our coast. The entire 
amount of knowledge, even with those who recognized them when seen, amounted only to the 
vague term “animal flowers.” That they were animal forms, our few science-reading folks 
had learned from the science news and gossip that was wafted over from the more scientific 
centres of England and the continent. 
The great branch that embraces the Shell-fish — technically the Mollusca — had through 
various causes become, to a certain extent, familiar. Our clams and oysters were certainly 
