May 24,1924 Poly embryonic Development of Platygaster vernalis 
835 
only 18 m in diameter. Two such germs are represented in the polyblastula illus¬ 
trated in Plate 5, B. These germs have failed to develop, and will degenerate. 
They are similar to the pseudogerms described by the writers (8, 4) in Copido - 
soma gelechiae and in Platygaster hiemalis. Pseudogerms apparently do not occur 
in all P. vernalis parasite bodies. The writers believe that they are developed as 
a result of total division of a daughter germ, and that the resulting components 
do not contain sufficient potential elements to allow them to mature. 
At about the twenty-fourth day the polyblastula is usually elongate. The 
one represented by Plate 6, A, measures approximately 0.4 mm. in length and 
0.07 mm. in width. It contains seven blastulas which are about ready to begin 
organogeny of the embryo. In this particular parasite body the paranuclear 
masses are found at each end. In the less elongate but more ovoid parasite 
bodies the paranuclear masses continue to be distributed regularly throughout 
the trophamnion. 
THE POLYEMBRYONAL MASS 
Between the twenty-sixth and thirty-second days after the egg has been de¬ 
posited the parasite body represents a typical polyembryonal mass. During 
this period organogeny of the embryos takes place. The parasite body is usually 
found intact in one end of the mid-intestine of the host at this time (PI. 7, B), 
although occasionally it may become split up into two or three secondary poly¬ 
embryonal masses. 
A twenty-seven day old parasite body is illustrated in Plate 6, B. This para¬ 
site body measures approximately 0.52 by 0.19 mm. The embryos continue 
to be held together by the trophamnion, which is less dense than in the preceding 
stages. The paranuclear masses have increased in size, but these, too, are less 
concentrated. 
The organogeny of the embryos, as far as has been determined in a general 
way, takes place similarly to that described by Marchal (5, 6) for Polygnotus 
minutus and other Platygasters and by Silvestri ( 9 ) for Platygaster dryomyiae; 
and it will therefore not be referred to in detail. The blastulas become some¬ 
what oval (PI. 6, A) before the embryonic layers are differentiated. Prior to 
the formation of the mesenteron the embryos assume the U-shape (PI. 6, B) 
described for other polyembryonic Hymenoptera, and then straighten out to 
form the primary larval stage (PI. 7, B). During organogeny the embryos 
increase in size from 0.09 mm. in length, when they are somewhat U-shaped, to 
approximately 0.14 mm., when they resemble typical primary larvae. 
The final stage of the polyembryonal mass is illustrated in Plate 7, B, which 
represents a section through a parasite body at about the thirty-second day. 
The parasite body measures 0.8 by 0.4 mm. The embryos are in reality fully 
formed primary larvae which have not yet taken any food, and measure approxi¬ 
mately 0.23 by 0.07 mm. The fixed host in which this polyembryonal mass is 
found measures 3.8 mm. in length, while its mid-intestine measures 2.1 by 0.47 
mm. 
* About the thirty-fourth day the membranelike trophamnion is ruptured by 
the first feeding of the primary larvae, whereupon the larvae are set free in the 
mid-intestine of the host (PI. 1, D). 
SUMMARY AND DISCUSSION OF CLEAVAGE TO LARVAL STAGES 
It has been demonstrated above that the egg of Platygaster vernalis is organ¬ 
ized into a typical poly germ, and finally into a polyembryonal mass, during the 
course of its later development, and before the newly formed primary larvae 
are set free. This development takes place entirely in the mid-intestine of the 
