PROGRESS OF MICROSCOPICAL SCIENCE. 
257 
Liverpool Microscopical Society, states that in " answer to the inquiry 
in a recent number (xiugust), as to the Volvox only being met with in 
June, in my experience I have met with them this year in May, and 
every month up to the present, and last year I certainly met with 
them in September. With respect to the Rotifers in Volvox, they are 
mostly found in the latter months. I have seen specimens almost 
daily the last three weeks, and not only Rotifers, but Rotifers in the 
egg, showing movement of the cilia and of the gizzard, and also eggs 
not so far developed. In one Volvox which I examined last night I 
saw three active Rotifers, two eggs showing movement, four eggs 
similar but quiescent, and four green spheres ; thirteen in all. There 
is, in my opinion, no question that some Rotifers are developed in the 
Volvox. The study of the Volvox at this particular time is well 
worthy of the attention of the microscopist." 
The Development of the House-fly. — This, v/hich was very thoroughly 
worked out in the Boston Societies' Reports a couple of years ago, has 
had an interesting paper devoted to it in the August number of the 
' American Naturalist,' by the same writer, Mr. A. S. Packard, jun. 
After describing the different methods adopted by him to secure an 
abundance of the ova, the writer goes on to describe a mode of exposing 
manure, which seems to have been very successful. Then he says : 
" The egg of the house-fly is long, slender, cylindrical, and a little 
smaller at the anterior end than at the other. It is • 04-* 05 of an inch 
long, and about one-quarter as thick. The shell is so dense that the 
early embryonic phases could not be watched, but enough was seen to 
enable us to determine that the mode of growth in the egg is nearly 
the same as that of the flesh-fly, as observed by Dr. Weismann. The 
eggs thus laid were found to hatch twenty-four hours later. In con- 
finement they required from five to ten hours more, and the maggots 
hatched in confinement were smaller than those reared from eggs 
deposited in warm manure. Certain worms reared also in too dry 
manure were nearly one-half smaller than those bred in more favour- 
able circumstances. For several days the worms living in this dry 
manure did not grow sensibly. Too direct warmth, but more espe- 
cially the want of sufficient moisture, and consequently of available 
semi-liquid fluid, seemed to cause them to become dwarfed. It is 
evident that heat and moisture are required for the normal develop- 
ment of the fly, as they are for nearly all insects. The maggot molts 
twice, consequently there are three stages of development, and it 
becomes sensibly larger at each stage. After remaining in the first 
stage for one day it molts, and differs from the j^receding stage only in 
being a little larger, and in the addition of the spiracle near the head. 
After remaining in this stage from twenty-four to thirty-six hours, it 
sheds its skin and enters upon the third stage, which lasts three or four 
days. The body is long and slender, somewhat conical, the head and 
mouth-parts being rudimentary. The end of the body is truncated, 
and bears two short tubercles or spiracles. If we enlarge one of 
these circular breathing holes we may see three sinuous openings, the 
edges of which are armed with fine projections, forming a rude sieve 
for the exclusion of dust and dirt. With these spiracles connect the 
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