302 ECOLOGY 
Slope, kind of soil, and soil moisture are factors governing the 
deficiency or absence of eggs. A deficiency or excess in any one of 
these respects decreases the number of eggs laid, or causes them not to 
be laid at all. The animals are in the condition for egg-laying for but a 
short period. 
d) Method of selection—It has been determined by opening holes 
that eggs are not laid in all, and in one case the first holes made by the 
female were empty. This would tend to show that the female beetle 
tries the soil before laying the eggs, but I have not been able in other 
cases to determine whether the first holes contained eggs or not. To 
determine this, it would be necessary to watch a female all of the time 
during several days. 
3. LAW OF TOLERATION (55) 
Repeated experiments with several species have shown results 
similar to those shown in Table LX VIII, and we have concluded that the 
egg-laying place of the tiger-beetles is their true habitat. The tiger- 
beetles which lay eggs in soil do so only when the surrounding tempera- 
ture and light are both suitable, the soil moist and probably also warm. 
The soil must satisfy the ovipositor (egg-laying organ) tests with respect 
to several factors. Egg-laying, the positive reaction, is then probably 
a response to several factors. Furthermore, after the eggs are laid, the 
conditions favorable for egg-laying must continue for about two weeks 
if the eggs are to hatch and the larvae reach the surface. The success 
of reproduction depends upon the qualitative and quantitative com- 
pleteness of the complex of conditions. This complete complex is called 
the ecological optimum. The negative reaction, on the other hand, appears 
to be different. The absence of eggs, the number of failures to lay, and 
therefore the number of eggs laid in any situation, can be controlled by 
qualitative or quantitative conditions with respect to any one of several 
factors. The presence, absence, or number of eggs laid may be governed 
by a single factor. 
For example, all other conditions being optimum, moisture may 
control the presence, absence, or number of eggs laid. If the moisture 
be optimum, the maximum number of eggs will be laid. If it is too 
great few or no eggs will be laid. This factor then controls according 
as it is near the optimum, or near either the maximum or minimum 
tolerated by the species. It is, however, not necessary that but a single 
factor should deviate; the effect is similar or more pronounced if several 
vary. 
