444 NHW YORK STATE MUSEUM 
tennae filiform, about equal to the body in length; wing ex- 
panse 20 to 40 mm, hind wings somewhat less. 
The males are usually a little smaller than the females. 
Larva. Suited for aquatic life. 20 to 30 mm long when full 
grown; tapering from head to the caudal end of abdomen; head 
and thorax yellow on dorsal side, mesothorax and metathorax 
bearing some light brown markings; the appendages of the head 
| and the eyes brown; abdominal seg- 
ments brown on the dorsal side and 
Siatks somewhat on the ventral side; first. 
seven segments of the abdomen cach 
supplied with a pair of five jointed, 
lateral appendages, evidently traca- 
eal gills, each with two rows of deli- 
cate hairs [fig. 20]; within these 
thin, white walled, gill appendages. 
are seen finely divided trachea; from 
the last abdominal segment is a 
single caudal appendage similar to 
Chautiodes but longer than the lateral ones and 
Fig. 20 Eggs of Sialididae not jointed and supplied with two 
large branching trachea and four 
rows of delicate hairs. This structure may indicate, as Miall 
has suggested, that the caudal appendage may have been 
formed by the fusion of two lateral appendages. There is a 
pair of minute spiracles present on each abdominal segment 
except the last. Each antenna has five segments, but the basal 
one if often obscure. 
On the dorsal side of the larva of S.infumata the segments 
are translucent, often showing the viscera. The lateral lobes 
of the abdominal segments are so transparent that the particles 
of blood may be seen and the pulsations of the heart may be 
counted. I found the number of pulsations to vary somewhat, 
but the average is about 10 a minute. Oenocytes with the finest 
branches of tracheoles leading to them are so plainly visible that 
they can be photographed. 
Eggs. The eggs of S. lutaria, the most common species 
in Europe, have been briefly described by Miall [1895] as “ dark 
brown, several hundred in one cluster, cylindrical with rounded 
ends, and closely packed together; from the free end of each egg 
a small, pointed and whitish projection is given off.” The eggs 
of our most common species, S.infumata, have been found in 
great numbers. They agree with the above description. The 
“whitish projection,” or micropylar projection, is not knobbed 
at the end, but the distal portion, which may be the micropylar 
surface, is cylindric in form, with a short, narrow pedicel at the 
point of attachment to the eggshell. 
