126 Dr Rusconi’s Observations on the Natural History 
tion, the author adheres to the opinion of Spallanzani. With 
respect to the others, he will confine himself to the facts he ob- 
served in relation to those questions, and leave the reader to de- 
cide for himself. 
In order to compare the changes going on exteriorly with 
those which might take place within, at the different periods of 
development, the author collected, on the same day, many eggs 
of the flat-tailed salamander, which had been mostly laid under 
his eye. He then put these eggs into two separate vessels — 
in one vessel, those eggs which should show the exterior changes ; 
in the other, those which he meant to sacrifice, in order to see 
the changes that go on internally. With these last, he put al- 
so some of the eggs of the little salamander, with the view of 
making comparisons. When the embryo, which he regarded as 
the type of the exterior changes, had attained to the degree of 
development indicated in Fig. 3d May, he drew from the 
other vessel another embryo which was at the same point of de- 
velopment ; and after having disengaged him entirely from his 
envelope, by means of two fine needles provided for the purpose, 
he placed him altogether alone in another vessel, in which there 
were no leaves of the Persicaria present. Whilst he was tearing 
the envelope, the embryo moved, and changed his position two 
or three times ; but as soon as he was put into the vessel, he 
dropped at once, with the body extended, to the bottom of the 
water, and remained motionless. Three hours after, it was ob- 
served that he had changed his position, and turned himself on 
the opposite side. In a word, he changed from time to time his 
position, as the embryos, while yet retained in their envelopes, 
do ; and his development continued, like theirs, without present- 
ing any difference. 
In proportion as the embryo of the salamander increases in 
size, its envelope becomes freed from the viscid matter with 
which it was besmeared, is dilated, and at length thinned to such 
a degree, that when the salamander is hatched, this membrane 
is reduced to an extremely fine pellicle. During its dilatation, 
the surrounding water passes through the walls of the mem- 
brane as through a filter ; so that the envelope, in all the stages 
of evolution, is always stretched, and filled with a very limpid 
fluid. The author could never see the smallest appearance of 
2 
