90 THE BIOLOGY OF THE SEASONS 



absence of certain characters that fit the latter insects for 

 their industrial life ; the hind tibiae [fourth joints of the leg] 

 have no smooth space for the conveyance of pollen, and, so 

 far as is known, there are only two sexes males and perfect 

 females. The Bombus and Psithyrus live together on the 

 best terms, and it appears probable that the latter do the 

 former no harm beyond appropriating a portion of their food 

 supplies. Schmiedeknecht says they are commensals, not 

 parasites ; but it must be admitted that singularly few 

 descriptions of the habits and life-histories of these interest- 

 ing insects have been recorded " (Sharp, loc. cit. p. 59). 



When there are too many guests, the family remains 

 small, but the relations of host and guest remain quite 

 friendly. The arrival of a new guest creates apparent 

 excitement, but there seems to be some fascination about the 

 big, lazy intruder. A well-established friend of the family 

 is said to resent the appearance of a newcomer. Altogether, 

 the association is a strange riddle. 



Humble-bees are very familiar animals, but there is still 

 much to be learned in regard to their ways what deter- 

 mines the production of workers, drones, or queens, what 

 time is required for the development of each, what deter- 

 mines the occasional parthenogenesis of workers, and so on. 

 These and other points, such as the great variability in the 

 colour of the abundant hair, require further investigation, 

 which is sure to be richly rewarded. 



It is impossible to pass from the humble-bee without 

 noticing the interesting position it occupies in the evolu- 

 tionary series of bees. Let us run up the scale. 



First, there are solitary bees like the leaf-cutter, 

 Megachile, who bores a tunnel in wood, lines the end of it 

 with neatly cut pieces of rose-leaf, deposits pollen, nectar, 

 and eggs, shuts the door, and flies away. 



Second, there is a stage represented by a rare bee, 



