1058 The American Naturalist. [December, 
new family of fossil beetles established by Schlechtendahl in a recent 
paper on the fossil insects of Rott on the Rhine (Abh. Naturf. Ges. 
Halle, XX). It is named Paleogyrinid:, and the type shows a com. 
bination of the characters of Gyrinide and Dytiscide. “ Extinct 
types of insects of as high a grade as families are extremely rare in the 
tertiaries.” 
Reversal of Position in Insect Embryos.— Dr. G. A. Chap- 
man summarizes’ his own and others’ observations on the phenomena 
associated with the change of position that occurs in the young lepidop- 
terous lary within the shell before hatching. “In all cases the larva 
first appears on the surface of the yelk-mass as a flat plate, of which 
the central line is the middle of the ventral surface, and the margins 
are the two sides of the dorsum, still far apart. These margins, how- 
ever, rapidly curl in and, at the head and tail, the young embryo soon 
has the cylindrical form we associate with the larva, but centrally, 
there remains a wide opening through which the mass of the yelk is 
continuous: with that portion of it contained in a central cavity of the 
larva; this central cavity is the future alimentary canal, not yet pro- 
vided, however, with any opening towards either the head or the tail, 
The communication between the intestinal cavity and the yelk sac 
gradually becomes smaller, and portions of yelk leave the sac and pass 
into the intestine, and contribute to the growth of the embryo. Dur- 
ing this period, it is easy, in flat eggs like those of the Pyralides, Tor- 
trices, Limacodes, etc., to see the embryo curled around a greater or 
less portion of the yelk sac, with its ventral surface towards the mar- 
gin of the egg, and its dorsal surface (aspect rather than surface, as 
the surface is still broken by the umbilical opening) applied to the 
yelk sac. There is a little variation in the degree to which the yelk 
disappears before the umbilical opening closes, but when this takes 
place-the larva forms a horseshoe or circle, with the venter towards the 
shell wall and its anterior and posterior extremities in contact. At 
this period, also, there are a varying number of globules of yelk free 
in the egg cavity around the larva; whether these are set free by the 
movement of the larva that now takes place, or still later by the jaw 
action of the larva, I am not sure, but after the movement has taken 
place the young larva swallows these; this swallowing of the remaining 
| yelk may indeed be regarded as a first step towards eating its way out of 
the egg. Before the closing of the umbilical opening, the embryo may 
be regarded as an appendage to the yelk sac, attached thereto by its 
*Entomologist's Record, Oct. 15, 1894. 
