74 
Psyche 
[April 
effects which cause the insect to assume this position irrespective 
of the immediate presence of the causative stimulus. 
One other explanation may be offered here: The aphid 
possibly assumes this position for mechanical advantage, in the 
way of bringing about optimum efficiency in the functions of the 
sucking mouth-parts, and of minimizing the strain on the muscles 
of the legs and other parts of the body which is occasioned by the 
insect’s having to remain in one position for considerable lengths 
of time while feeding. 
The fact that the aphids turn around and resume feeding in 
the reverse direction with respect to the plant when the tips of 
the tansy on which they are situated are bent indicates that this 
behavior of Macrosiphum has not been brought about as an 
adaptation to any peculiarity in the structure of the host. 
The characteristic feeding position of Macrosiphum tanaceti 
has also been observed by me in other species of Macrosiphum. 
It is interesting to note that the aphids of other genera which I 
have studied 3 do not seem to exhibit this peculiarity. They 
almost all indifferently assume any position while feeding. It 
may be mentioned, as a possible explanation of this difference in 
behavior, that these other aphids generally feed on the nether 
surface of broad leaves, or are otherwise protected from the direct 
rays of the sun. Thus the main stimulus which, as I have sug- 
gested above, is probably responsible for the characteristic 
position of the Macrosiphum species is suppressed in the case of 
the other aphids. 
Summary of Section III. 1. Macrosiphum tanaceti appears 
to be confined to a single host plant, Tanacetum vulgare. From 
early in the spring until late in the fall in Boston and vicinity, this 
aphid in diffierent instars is found feeding on the more succulent 
portions of the plant, principally on the growing regions of the 
stem. 
2. The head of the insect is. directed toward the ground 
3Anoecia, Lachnus, Longistigma, Drepanaphis, Drepanosiphum, Myzus, Eriosoma, un- 
identified aphids on Berberis vulgaris Linn., Celaslrus scandens Linn., Lylhrum salicaria Linn., 
Sherpherdia ( Elaeagnus ) argentea Nutt., and Viburnum sp., and others. 
