THE GROUXD BEE. 



35 



in the most compact way possible. On the head of the semi- 

 pupa, i. e., a transition state between the larva and pupa, there 

 are two prominent tubercles situated behind the simple ej^es, or 

 ocelli; these are deciduous organs, apparently aiding the insect 

 in moving about its cell. They disappear in the mature pupa. 



To those accustomed to rearing butterflies, and seeing the 

 chrysalis at once assuming its perfected shape, after the caterpil- 

 lar skin is thrown off, it may seem strange to hear one speak of a 

 "half-pupa," and of stages intermediate 

 between the larva and pupa. But the ex- 

 ternal changes of form, though rapidly 

 passed through, consisting apparently of a Fig. 31. 

 mere sloughing off of the outer skin, are 

 yet preceded by slow and very gradual 

 alterations of tissues, resulting from the 

 growth of cells. An inner layer of the 

 larva-skin separates from the outer, and, 

 by changes in the form of the muscles, is 

 drawn into different positions, such as is . 

 assumed by the pupa, which thus lies con- 

 cealed beneath the larva-skin. But a Fig. 29. 

 slight alteration is made in the general 

 form of the larva, consisting mostly of an 

 enlargement of the thoracic segments, 

 which is often overlooked, even by the 

 special student, though of great interest 

 to the philosophic naturalist. 



From Mr. Emerton's observations we 

 should judge that the pupa state lasted 

 from three to four weeks, as the larvae 

 began to transform the first of August, 

 and appeared during the last week of the 

 same month as perfect bees. 



The Andrena is seen as late as the first 

 weelc in September, and again early in 

 April, about the flowers of the willow. 

 It is one of the largest of its genus and a 

 common species. 



Having, in a very fragmentary way, sketched the life history 

 of our Andrena, and had some glimpses of its subterranean life, 

 let us now compare with it another genus of solitary bee 



Fig. 



Fig. 31. Larva of Halic- 

 tus parallolus. 



Fig. 29. Larva of Andre- 

 na vicina. 



Fig. 30. Pupa of Halic- 

 tus parallelus seen 

 from beneath. 



