Production of Human Generation, &c. 159 
To investigate this matter, we must have recourse to those 
monsters in which there is a deficiency of parts. 
There is a very material difference between the nature of 
the life of the more perfect animals, during their time of 
foetal existence, and after that they are born. In the latter 
state, the brain and nerves appear to be so essential, that any 
very considerable defect in them is incompatible with the 
well-being of the animal ; but in the uterine state, consi- 
derable deviations from the ordinary arrangement of parts, 
and such as cannot be endured after birth, are supported, 
without any inconvenience. 
The brain has been frequently found very incompletely 
formed, and sometimes not at all, yet still there have been 
nerves. In other cases, where the brain has been perfect, the 
spinal marrow has been deficient in a great part of its extent, 
and sometimes throughout. 
Both these occurrences are sufficient to prove, that, at any 
rate, that intimate connexion of the brain and nervous sys- 
tem, which takes place after birth, is not necessary for the 
formation of a body in other respects perfect. But still it 
would remain doubtful, whether any regular structure could 
be formed, without any vestige of either brain, or nerves ; 
and therefore without a possibility of their influence, in any 
manner, toward such structure. 
The monster now under consideration is so extremely 
simple, in this respect, that it cannot be exceeded by the most 
simple animal known. 
It may be objected, however, that there might be brain, or 
nervous fibres, in this monster, but that they might, in the 
dissection, be destroyed. But, in the first place, I beg leave 
Ye 
