6 
{ add to this description, some physiological remarks, in 
reference to the egg-tooth, in comparison with other organs of 
living organisms. 
We often see in physiological papers the various organs and 
systems of organs, of the animal and vegetable body, treated 
in reference to the importance they bear to the whole economy 
of the living being. Every physician knows that there are 
many organs, most of them exterior ones, for instance organs 
of touch or locomotion, as fingers, hands, arms and legs, or 
even organs of the higher senses, as the tongue, nose and eye, 
which may be hurt or totally destroyed, without destroying 
necessarily the life, or even the health of the remaining organ- 
ism. We know from experiments made in physiological 
laboratories, upon mammals or other vertebrates, that even some 
interior organs, as for instance, certain parts of the brain, the 
whole spleen, &c., may often be taken out without interfering 
with the health of the animal; while on the contrary there are 
other organs, as the medulla oblongata, the heart and the 
intestines, which are so important for sustaining life, that 
frequently a slight wounding of them is followed by death. 
This is one way of viewing organs, and certainly a very practi- 
cal one. But there is another, if not so practical, certainly as 
philosophical, namely to compare the organs with one another, 
with reference to the history of the life of the individual, when 
they make their first appearance, when they begin to work, 
when they stop working, and when they fade away. We will 
allude here only to some instances. Let us consider any of 
the Vertebrates, after the fecundation of the egg, by the 
penetrating of the Zoospermia into it, and after the segmenta- 
tion of the yolk is over. We see, as the first signs of the new — 
being, a furrow more open on one side than on the other. 
This furrow is the birthplace of the future brain and dorsal 
marrow, the more open part at the anterior end being the 
future brain. 
The sidewalls of this furrow begin to grow upwards and 
meet above, thus making a tube of the furrow; and it is very — 
remarkable, that this closing takes place first in the very place, 
where the medulla oblongata is afterwards formed, this most 
delicate and most important part of the organism. Soon. 
after this furrow is closed, we see a longitudinal, tube-like 
heart beating; and an intestine formed. We will not go into 
further details. We already see that just those organs, which 
are the principal supporters of the animal and vegetable life of 
the vertebrates, and which therefore remain through its life, 
are also those, which first make their appearance in the devel- 
