81 



I 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 oat 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. Bat 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 farrow 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- 



