on the larvae of Muscidae. 21 
laid out at intervals during such years, produced the largest number 
of Oynomyiae from the middle to the end of May, with a minimum 
about the beginning of June, from which time the blue-bottle began 
to grow in numbers at the expense of Oynomyia,* which ceased to 
appear about the end of June. The only chance for Oynomyia 
therefore is in the spring, as long as its competitors are less nume- 
rous, and especially in such years when, for some reason, the blue- 
bottle is rare, or appears later. We have here an instance of the 
dependence of the propagation of a fly on the number of eggs it is 
capable to lay. — 
Now about flies developing in dung (coprophagous) ı). 
We begin with Musca domestica, the common house-fly, although 
on account of its favored, domestie position, it does not, as will be 
shown, follow the common rule of other dung-flies. Notwithstanding 
the difference in the environment, the development of M. domestica 
shows some resemblance to that of the blue-bottle fly. It lays about 
120—160 small eggs, from which in about 24 hours the larvae in 
the first stage of development are hatched; they are characterized 
by very small stigmatic horny plates, with a single, heart-shaped 
breathing-fissure (like that of the blue-bottle); the larva remains in 
this state about a day, and then enters the second stage, characte- 
rized by stigmatie plates with two fissures, almost exactly like those 
of the blue-bottle. After another day the larva reaches the third 
stage, with still larger stigmatie plates, each of which has two brea- 
thing fissures of a peculiar shape, distincetive of the species: 
a meandering, serpentine line running parallel to the outer ring of 
the horny plate (Fig. 2). In other respects the larva of Musca 
domestica is exceedingly like that of the field-fly (Musca corvina) 
and also of the meadow-fly (Dasyphora pratorum). The differences 
are slisht. The larva of Musca domestica difters from that of 
M. corvina in the shape of the anterior spiracles, which have six rays 
in the former, and twelve in M. corvina. The posterior stigmatic 
plates of Musca corvina are very large, in comparison to those of 
‚the two other species; in M. domestica they are small and more 
distant from each other; in Dasyphora pratorum they are also 
smaller than in M. corvina, and still nearer to each other. In the 
perfect state Musca domestica and corvina are exceedingly alike; 
there is a slight difference only in the structure of the front and in 
the coloring. x 
1) The authors researches extend merely to the fecal matters of 
men and horned cattle. 
