44 REVIEWS. 
before pupation, at least Ganin could never find any Platygaster 
in any other situation than in the larva of Cecidomyia. 
` The eggs of Platygaster taken from the ovary of a female two 
or three days after leaving the pupa, are long, oval, with a long 
thin stalk, and a very elastic shell (chorion). During the develop- 
ment of the embryo the egg increases in size from ten to fifteen 
times its original bulk. The eggs of this and the other genera 
mentioned below, differ from those of other insects in wanting the ` | 
nutrient yolk-cells (ernihrungsdotter). The entire egg consists 
of the formative yolk-cells (bildungsdotter). This formative yolk 
appears as a pale, thick, structureless protoplasm, in which the 
so-called yolk cellules, or nuclei (dotterkérnchen), are wanting. In 
the central part of the egg we find in the direction of its longer 
axis, a considerable number of transparent molecular cellules ; but 
at the periphery of the egg, these most minute of all organized 
histological structures are wanting. The protoplasm of the egg is 
wholly structureless. 
The ovarian egg is formed by the growth of a cell lying at 
the hinder pole of the egg tube. This egg-cell has at first no 
membrane ; its transparent, viscid protoplasm gives origin to the 
yolk. The small, sharply contoured nucleus of the egg is no other 
than the primitive vesicle of the egg. The primitive vesicle dis- 
appears when the imago leaves the pupa. Its ground substance, as 
also that of the granular portion, resembling the white of an egg, 
is converted into a fine, molecular mass, which is found in the 
central part of the ripe egg. The number of egg tubes in each 
ovary is thirty, corresponding to the number of eggs in each tube. 
‘The ovary of Platygaster differs from that of all other insects 
in that it is a closed tube, or sac. Hence it follows that at every 
time an egg is laid, the egg tube is ruptured. This was also ob- 
served in the Sheep tick (Melophagus) by Leuckart, and in certain 
flies (Limnobia, Psychoda, and Mycetobia) by Ganin. 
The earliest stage observed after the egg is laid, is that in which 
thè egg contains a single cell with a nucleus and nucleolus. Out of 
this cell (Fig. 16 A, a) arise two other cells. The central cell 
(@) gives origin to the embryo. The two outer ones multiply 
by subdivision and form the embryonal membrane, or ‘ amnion,” 
which is a provisional envelope and does not assist in building up 
the body of the germ. The central single cell, however, multiplies 
by the subdivision of its nucleus, thus building up the body of the 
ae) 
