1906] 
GIRAULT—TRICHOGRAMMA PRETIOSA RILEY 
147 
c. A female of pretiona confined at 3: 46 i>. m., September 27th with nineteen 
(19) hosts, then hatching. Thirteen (13) of these hosts were successfully {)arasitizcd. 
A control lot of hosts hatching at 3 i>. M., the same day. Hence oviposition effective 
uj) to within 4 or 5 hours, at the most, of e.xclusion of the host. 
d. Five (.5) hosts nearly ready to e.xclude, the perfect embryos visible, were 
exposed to a female parasite at 10: 15 M., Se])tember 2Sth. One of the hosts 
excluded at 10: 55 .\. M. The other four (4) were blackened by the effects of parasi- 
tism by October first, or i)reviously. These four yielded adult parasites later. Con- 
trol lot of hosts excluding at 10 a. m., September 28th. Hence oviposition of pirii- 
osa effective u]> to the moment of exclusion of the host. 
These experiments strongly indicate that parasitization is successful up to the 
very moment of exclusion of the host, despite the fact that the perfect embrvos of 
obftolefa are active ami very capable of caring for themselves. They are not conclu- 
sive, however. Other ex])criments performed, indicate that when the host embryo 
is fully formed, parasitization is less successful than otherwise, doubtless due to the 
greater vitality of the embryo. Hence, there appears to be a certain period in the 
development of the host, the period between the perfect formation of the embryo 
and exclusion, in which it is partially, not totally, immune from attack. 
8. Length of the period of oviposition. It was absolutely impossible to deter- 
mine this under an\lhing like natural conditions from the very nature of the case. 
From the evidence gathered in the laboratory, it is certain that the period of oviposi- 
tion is very short, but it is not felt that this evidence warrants a statement of definite 
limits. 
What conclusions are po.ssible may be induced from what is said in regard to this 
matter on a previous page. 
9. Changes undergone hy parasitized hosts. After being parasitized, the host 
eggs retain their normal appearance, until the egg of the parasite hatches, when they 
become characteristically blackened, an opaque or dull bluish black. They still 
retain their normal shape and size, and the color persists indefinitely, always serving 
to distinguish eggs that have been parasitized. After the emergence of the resulting 
parasite or parasites, through a rounded hole in the side of the host egg, the color 
and shape still persist, and so on until the empty shell is destroyed through natural 
agencies. The black color comes on gradually, the host at first becoming dusky, 
finally opaque and black-blue. Infertile hosts are affected in the same way. 
10. Length of the egg instar. If it is true that the black color of the host is due 
to the hatching of the parasite’s egg, then the following table shows lengths of the 
period of incubation at different times of the season of 1 904, as indicated by this 
