436 GENERAL PRINCIPLES 



ing in physiological processes connected with the organs of 

 reproduction. 



876. Practically the same may be said of the actions of the mud 

 dauber when building her mud nest and filling it with embalmed 

 spiders. Another example may be described. There is a fam- 

 ily of beetles (Cantharidae) which are parasitic on other insects 

 during the larval stages. In some cases (Sitaris) the eggs of the 

 beetle are deposited on the ground in the vicinity of a bumble- 

 bee's nest. A small active larva hatches from these eggs and 

 this larva reaches the nest of the bumblebee in a very peculiar 

 way. It does not seek the opening of the nest and thus make 

 its way in, but waits until some living object like the bumblebee 

 chances to come within reach, when it attaches itself to the legs 

 or hairs of the body and is thus carried into the nest. The 

 bumblebee builds a large cell of wax. This it fills with honey, 

 and then deposits an egg on the honey and seals up the cell. 

 At the moment when the egg is deposited the beetle larva 

 attaches itself to the egg and is thus sealed up in the cell with 

 the egg and honey. It first devours the egg, which requires al- 

 most eight days' time. Then it undergoes a metamorphosis, 

 after which it is adapted for feeding upon honey, which it could 

 not do before. After about forty days' feeding on honey the 

 supply is exhausted and the larva undergoes a second meta- 

 morphosis. This is followed by several more metamorphoses, 

 after which the adult beetle (blister beetle) appears. The 

 notable thing about this life history is the means adopted by the 

 minute larvae for reaching the nest of the bee. They will often 

 attach themselves to other living objects, such as other insects 

 or even a camel's hair brush. When they do this they perish, 

 because they fail to reach the condition necessary for their 

 future development. These larvae are not taught what they 

 have to do to succeed; they cannot profit by the observation of 

 others, and they cannot learn from experience. They are 

 somehow impelled to attach themselves to other insects. If 



