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the Pieces neareft to the Tail are thofe which make 
the leaft Progrefs. Among this Number is chiefly to 
be reckoned the laft. As to the Firft, that which 
keeps the Head, though that is often the Piece which 
in an equal Time recovers the longeft Tail, yet does 
not this happen fo conftantly as to build a Rule upon 
it. My Obfervations have furnifhed me with more 
than one Proof of this. Neither is it a Rule, that 
all the intermediate Pieces, which have recovered 
Heads, will alfo recover Tails : I have Examples to 
the contrary. But what feems certain, is, that the 
State of the Worm, the Number of its Divifions, 
and other Circumflances, feem very much to influence 
all thofe Irregularities. 
The want of Nourifhment, or of fuch as is proper, 
may alfo be a Caufe, and that a very natural one, of 
like Variations. I faid above, that thofe Worms 
love to be in the Mud, and that they digeft it. 
Thofe Pieces which I left purpofely in clear Water, 
have ufually very well recovered what they wanted to 
become true Worms ; though afterwards they made 
but little Progrefs, and almoft all fucceflively perifhed. 
V. The learned Dr. Hales , in his excellent Vege- 
table Staticks, relates a curious Experiment ; by 
which he proves, that the Bones of Animals, when 
they are oflified to a certain Degree, do not grow 
any longer but at their Extremities. Many Obfer- 
vations have convinced me, that it is the fame with 
our Worms. The old Piece, I mean that which was 
originally cut from the Worm, does not itfelf 
lengthen, but its Increafe is only owing to the 
Growth of thofe additional Parts, that put out at each 
Extremity. 
VI. It 
