154 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 4. NO. 4. 
On September 18th of the same year I came across a very 
young larva and an empty egg-shell of Lcucospis affinis in a nest 
belonging to a third species of Osmia, O. simUlima. The larva of 
the parasite was crawling around on a dead larva of Osmia, it did 
not seem to thrive on this kind of a diet, and died two days later. 
A cell of another nest of O. simUlima collected on the same date 
contained also a dead larva of the bee inside of its cocoon and an 
egg of the parasite adherent to the inner wall of the cocoon. These 
two nests of 0. simUlima were found at Milwaukee in small pieces 
of driftwood lying on the beach of Lake Michigan. 
The most valuable information was obtained from a nest of 
Osmia atrk cut vis situated in a broken off dry branch. A specimen 
of Leucospis affinis was observed ovipositing in three different 
places close together near the end of the branch between n a. if. 
and 12:15 p. m. on July nth of the present year. On opening 
the nest two days later it was found to contain three cells of Osmia 
situated about 7 mm. below the upper surface of the branch in the 
old gallery of a coleopterous larva running longitudinally. These 
7 mm. represent the distance the ovipositor of the parasite had to 
travel through solid wood before reaching the cavity of the cell. 
In this, and in the other two species of Osmia referred to above, 
a paste consisting of chewed pieces of leaves is made use of in the 
construction of the partitions between the cells and the plug closing 
up the outer end of the gallery. In the nest under consideration 
the plug had a length of 9 mm. and each of the three cells one of 
7 mm., giving the entire structure a length of 3 cm. 
In each of the cells an egg of the parasite had been deposited, 
and it is an interesting fact to be recalled further on that while the 
lowest cell contained a full-grown bee-larva just beginning to spin 
its cocoon, and the middle cell also a full-grown one, the larva of 
the uppermost cell had only reached half of its size, and still had a 
fair amount of food to dispose of. 
Mode of opposition. While in search of a suitable spot for 
inserting its ovipositor the parasite was observed walking slowly 
over the branch in the region outside of the Osmia nest, palpating 
the surface with its antennae, and at the same time moving the 
abdomen upward and downward. The antennas alternate in their 
palpating movements, the one going upwards while the other goes 
downwards. As soon as a spot has been selected the insect turns 
