THE DEVELOPMENT OF THE FROG. bel 
length (if a dry system) is much shorter than ;}, inch, or if an im- 
mersion system, than 51; inch, is altogether problematical. 
The actual powers of the microscope (in the strict sense of 
correct and useful power) are, in my opinion, exhausted at these 
limits, so long, that is, as no circumstances of moment are brought 
forward which change the bearing of present theory. There exists 
no microscope in which there has been seen, or will be seen, any 
structure which really exists in the object, and is inherent in its 
nature, that a normal eye cannot recognize with a sharply defining 
immersion lens magnifying 800 times. Reports of extraordinary 
performances (especially from England) of unusually high power 
sig inch?) are not of such a character as to induce me to change 
my opinion and lead me into similar error, for the superiority of 
such lenses is said to have been proved upon objects to which the 
results of my observations unreservedly apply, and which are said 
to appear under such amplification as everyone who can understand 
and give an account to himself of the optical conditions of such 
performances must know to be wholly illusory.—From Proceedings 
of the Bristol Naturalists’ Society, New Series, vol. i., part 2. 
THE DEVELOPMENT OF THE FROG. 
By Mr. Morrison. 
A paper read before the Bolton Microscopical Society. 
(Continued from page 162.) 
HE hind feet protrude outside the body of No. 1 at 50 days; 
No. 2, 60 days; No. 3, 70 days; No. 4, go days; while they 
stand out from the body ¥% of an inch at 60, 70, 90, and 120 
days respectively. At this time there is a rapid development in 
No. 1, at 68 days the hind legs are almost full out, and the fore 
feet are out 4% of aninch. The mouth is getting enlarged in size, 
and the horny lips are being replaced by teeth growing from a 
palate. The intestines get shorter, and this forms one of the 
strongest points in support of its vegetable feeding, while the lungs 
proper, which were only rudimentary and seemingly solid, are 
rapidly growing and expanding. ‘The pulmonary organs or vessels 
also increase in number, while the bronchial vessels are shrinking, 
and getting beautifully less. These changes indicate an interesting 
fact that the respiratory organs of our tadpole are quickly becoming 
those of an air breathing animal, and the body is fast shrinking 
into the true frog shape ; the tail is being rapidly absorbed, and 
sending out the legs to their full length. 
