1917] Smith—Leaf-Oviposition Among the Parasitic Hymenoptera 67 
surface of the leaf at one end. Hatching takes place in seven 
to ten days and the first stage larva is of the planidium type de- 
scribed in the above mentioned paper. For several days previous 
to hatching the dark-colored planidium can be plainly discerned 
through the transparent egg-shell. The planidium is active imme- 
diately upon hatching, crawling rapidly about, but soon it attaches 
itself to the leaf by means of the caudal sucker and stands out at 
right angles to the surface. In this position it remains for days 
at a time, motionless, excepting when some insect comes within 
its reach, when it suddenly becomes frantically active, reaching and 
swaying back and forth in its attempt to attach itself to the pro- 
spective host. If the latter should unfortunately come too near, the 
planidium attaches itself with lightening-like quickness to a hair or 
bristle of the host. It then leisurely crawls down the hair to the 
host’s body and attaches itself by its mouth-hooks. Quite often 
the planidia are found attached to the egg-stalk of Chrysopa, 
assuming a position at right angles to the axis of the stalk. This 
shows an interesting instinct in the planidium, since it may and 
actually does, as the writer has observed, waylay the young Chry- 
sopa larva as it leaves the egg and crawls down the stalk. The 
prescience of the mother Chrysopa in placing her eggs at the end 
of a long egg-stalk to overcome the cannibalistic propensities of 
her progeny is in this case their undoing, since the planidium at- 
tached to the Chrysopa egg-stalk is sure to reach its proper host, 
while those upon the surface of a leaf are quite as likely to attach 
themselves to an aphid or other insect.! 
The planidia are remarkably long-lived for such delicate crea- 
tures. I have had them live for a period of seventeen days with- 
out food of any kind and without changing their position. Those 
which are fortunate enough to become attached to a Chrysopa 
larva immediately, as mentioned above, crawl down the hair or 
bristle and by means of their mouthparts attach themselves to 
the skin of their host. Many of these planidia undoubtedly lose 
their opportunity to develop through the moulting of the Chry- 
sopa larva, although sometimes, as observed by the writer in the 
laboratory, they succeed in changing their position from the 
1 In a note in the Journal of Economic Entomology, Vol. 9, p. 510, Mr. M. T. Smulyan men- 
tions having found a Perilampus planidium on an aphid. Without doubt this is the young of a 
Chrysopa infesting species which attached itself to the wrong host. They will even grasp a 
camels hair brush if brought within their reach. 
