246 B. GRASSI AND A. SANDIAS. 
To Fritz MUtier, 
on his Jubilee. 
Catania, 1892. 
INTRODUCTION. 
Ir has been recognised by Darwin, in his immortal work on 
the ‘ Origin of Species,’ that the existence of insect commu- 
nities, composed of different castes (kings, queens, workers, 
soldiers, and the like), furnishes his opponents with a trenchant 
weapon. Now these communities actually consist not merely 
of fertile forms (kings and queens), but of sterile forms 
(workers, soldiers, &c.), distinguished by important modifica- 
tions of structure and marvellous instincts, none of which are 
to be found in their parents. The sterile progeny would there- 
fore appear to be uninfluenced by one of the prime factors in 
the struggle for existence, that of heredity, owing to the im- 
possibility of transmitting to the offspring such modifications 
of structure or instinct as may be gradually acquired; and 
Darwin himself admits that it required great confidence in his 
theory not to renounce it in the face of this objection. 
I have had to deal shortly with this question on another 
occasion with regard to bees, for which I have observed that 
the cause of their apparent deviation from the normal rule 
may possibly be found in the existence of workers capable of 
oviposition, which apply themselves to all the tasks of the 
colony, and possess the characteristics of true workers, with 
the single difference that they lay parthenogenetic male ova. 
The males which hatch from these eggs would then transmit 
to the female ova—laid, as we know, by the queen—the cha- 
racteristic properties of the worker.! 
1 Darwin, however, explains the phenomenon by a very ingenious com- 
parison. ‘ According to M. Verlot,’ he writes, “some varieties of the 
double annual stock, from having been long and carefully selected to the right 
degree, always produce a large proportion of seedlings bearing double and 
quite sterile flowers ; but they likewise yield some single and fertile plants. 
These latter, by which alone the variety can be propagated, may be compared 
