834 
Journal of Agricultural Research 
Vol. XXVIII, No. 8 
If all the nuclei divided regularly at the fourth cleavage the polygerm should 
contain sixteen germs. If only seven of the eight embryonic nuclei divided at 
the fourth cleavage, the polygerm would contain only fifteen germs. Difficulties 
of interpretation as to whether each germ is originally composed of a single 
cleavage nucleus are often encountered by reason of the fact that the single 
nucleus of a germ divides to form a binucleated germ before others of the same 
poly germ divide. Moreover, the nuclei are often so disposed (one above the 
other) and the germ membrane is sometimes so indistinct, that it appears as if 
some germs might originally be composed of two embryonic or cleavage nuclei. 
The contention that a germ originates from a single embryonic nucleus in this 
polyembryonic species is based upon a study of such preparations as are illus¬ 
trated by Plate 4, A and B. Figure A shows that most of the nuclei are each sur¬ 
rounded by a portion of the embryonic cytoplasm, which is in turn encom- - 
passed by a membrane. Figure B represents a later stage, and shows two germs 
containing but a single nucleus each, while two other germs contain two nuclei 
each as a result of a recent division of the original nucleus of each of the two germs. 
A fifth germ contains four nuclei, while a sixth has already advanced to the morula 
stage. 
The poly germ is either slightly ovoid or spherical at this time and measures ap¬ 
proximately 47 ju in its greatest diameter. The trophamnion now is no longer 
confined to the periphery of a central embryonic region but penetrates toward th e 
center of the polygerm so that it surrounds each germ. 
About the twelfth day the polygerm (PI. 4, C) measures about 57 n in diameter. 
With the increase in size of the polygerm there is also noted an increase in the 
size of each germ. At this stage certain of the germs divide in toto to form two 
daughter germs. Not all of the germs divide, and when division takes place 
the parent germ is usually composed of approximately eight nuclei. A similar 
division has been recorded by Marchal (5) in Polygnotus minutus and by the 
senior writer ( 3 ) in Copidosoma gelechiae. A typical case of germ division is 
illustrated in Plate 4, C. Here two of the four germs are daughter germs that 
are still in contact, and separated only by a very thin portion of the tropham¬ 
nion which filtered between them immediately after division. Henceforth the 
embryos develop rapidly into the blastula stage. 
THE POLYBLASTULA STAGE 
About thirteen days after oviposition the parasite body (PI. 4, E) represents 
a typical poly blastula stage. The germs have increased -both in size and in 
number of their nuclei. The nuclei become lodged in cells and are arranged 
regularly in the periphery of the germ, so that a median section through an embryo 
illustrates a true blastula. At the thirteenth day the polyblastula measures 
about 55 y in its greatest length and 45 /z in width. 
Between the thirteenth and eighteenth days the polyblastula increases in size 
until it measures about 75 n by 68 /z (PI. 4, F; PI. 5, A). The oval or spherical 
shape of the parasite body is maintained. During this interval the blastulas 
and the cavities in which they are found increase in size proportionately, as do 
the paranuclear masses of the trophamnion. The trophamnion also appears 
somewhat vacuolated. 
By the twentieth day the polyblastula measures when spherical about 114 
in diameter. At about this stage one observes definitely that all of the embryos 
are not approximately of the same size. Some of the embryos are normal blastu¬ 
las, while others are composed of but four to ten nuclei and are in reality in the 
germ stage. Instead of the cavities in which the germs are located measuring 
40 ix in diameter, as do those of the typical blastulaslof this age, they measure 
