34 2 
Journal of Agricultural Research 
Vol. XXV, No. 8 
During the fifth day the structure of the parasite body remains the 
same, but there is a notable increase in size of the parasite body, so 
that by the end of the fifth day the parasite body measures 22 juin length 
and 11.4 ju in width (PL 3, F). The paranuclear masses are larger and 
usually widely separated in the trophamnion. At this time the parasite 
body is entirely surrounded by host tissue. This condition is true at 
least of most of the parasite bodies in a particular host (that is, say, four 
of six eggs originally deposited in the host), but others are to be seen in 
the same host which are not surrounded by host tissue, these being in a 
retarded and inactive stage of development. The retarded developing 
forms will be referred to later. 
DIVISION WITHIN THE PARASITE BODY TO FORM TWIN GERMS 
About the sixth day after oviposition the parasite body departs from 
its previous oval shape and becomes more elongate. The assumption of 
this newer shape is due to a division of each of the two paranuclear 
masses to form four separate masses. Two paranuclear masses are now 
to be found near or at each end of the parasite body. 
A division of the embryonic region in some of lie parasite bodies to 
form two separate embryonic regions then takes place, two of the four 
embryonic nuclei becoming included with each half of the divided 
embryonic region (PI. 3, G). Each half of the embryonic region is now 
a true germ and is structurally the same as a 3-day-old parasite body 
after the first cleavage, since it is composed of two paranuclear masses 
and two embryonic nuclei in an embryonic region. No further division 
of the embryonic region or later developing blastula stages takes place; 
but each germ develops directly into the blastula and late embryo 
stages, and finally into a larva. The original egg (or parasite body) 
therefore develops into twin parasites. 
SEPARATION AND DEVELOPMENT OR GERMS 
Immediately after the division of the embryonic region to form twin 
germs, the trophamnion of the parasite body is still continuous (PI. 3, 
H). Indentations of the trophamnion between the twin germs are soon 
visible, however (PI. 3, G), and the two germs finally become structurally 
independent of each other. Henceforth each germ continues develop¬ 
ment by itself, although for a while both germs may continue to develop 
side by side until the blastula, or even a later stage, is reached, the 
two germs being held in contact or close together solely by the host 
tissue which surrounds them. 
After the twin germinal regions are formed, the two embryonic nuclei 
in each germ (PI. 3, G) divide and give rise to four embryonic nuclei 
(PI. 3, H; PI. 4, A). The embryonic region of each germ is spherical 
and measures about 12 ^ in diameter when the four embryonic nuclei are 
just formed. The next cleavage of the embryonic nuclei results in the 
production of 8 nuclei in each germ. After the third cleavage, when 
16 embryonic nuclei are to be found (PI. 4, B), the nuclei become ar¬ 
ranged in a circle (in section), thus assuming the typical early blastula 
stage. At this stage the embryonic region is still spherical and measures 
about 19.1 ijl in diameter. 
During the three cleavages of the embryonic nuclei the embryonic 
region of the germs is surrounded by the trophamnion. In the tro- 
