22 ©. R. Osten Sacken: on Mr. Portchinski's publications 
Considering the great resemblance between these two flies in 
the imago-state and in that of the mature larva, the very important 
differences in their mode of development are the more astonishing. 
Musca corvina -lays on dung only 24 comparatively large eggs of 
a very peculiar shape, and not, like the house-fly 120—160 very 
small eggs of the ordinary shape. — These eggs are about one and 
a half millimeters long, and have, beyond that length, an elongated, 
curved appendage, about two-thirds of the length of the egg, which, 
in the mature state has a dark color (fie. 5). 
s Musca corvina is not the only one among the dung-flies which 
lays a small number of large eggs. Pyrellia serena and Grapho- 
myia maculata do not lay more than 44 eggs, but they too are of 
a large size. Sarcophaga haematodes, viviparous like its congeners, 
lays 40 large larvae; Myospila meditabunda, Mesembrina mystacea 
and Spilogaster angelicae lay only 24 eggs each, and often less; 
the size of the eggs is 1,5 mm. for the first (the fly being 6 mm. 
long); 4 mm. for the second (length of the fly 12,5 mm.); 2 mm. for 
the third (length of the fly 6,5 mm.). The hatching of these large 
eggs, and the further development of the larvae, was observed on 
specimens of M. meditabunda, a fly which very easily lays its eggs 
in captivity. The egg of M. meditabunda is not unlike that of 
M. corvina, only the characteristic black appendage of the latter is 
much 'shorter here and its curvature much stronger; from this 
appendage a’ black stripe runs along the ventral side of the egg to 
its opposite end (fig. 6); a heap of these eggs look to the naked 
eye more like a heap of minute pupae. In about 24 hours larvae 
are hatched, with-the posterior spiracles already described before 
as characteristic of the first stage. But the next stage of the larva 
is not the second, but the third, characterized by posterior spiracles 
with three straight, slightly converging, slits. The passage from the 
first to the third stage is immediate, because a short time before it 
takes place the stigmata with the three slits become visible under 
the integument, alongside of the characteristie stighata of the first 
stage. After a very short larva-period, the pupa-state begins. N 
From the great resemblance of the eges of M. corvina to those 
of M. meditabunda, in their shape and size, as well as in their 
number, the inference may be drawn that the development of their 
larvae follows the same rule, that is, that the second larva- stage is 
omitted in M. corvina as it is in M. meditabunda. And thus, 
although M. corvina, as imago, is very like M. domestica its meta- 
morphosis is very different: 
M. domestica lays 120—160 small eggs, producing larvae which - 
undergo three stages of development. 
