The Theory of Parasitism 



To generalities, which are necessarily 

 vague, we will add some precise facts, A 

 certain Stelis {Stelis nasuta, Latr.) is a 

 parasite of the Chalicodoma of the Walls. 

 When the Mason-bee has finished building 

 her dome of cells upon her pebble, the para- 

 site appears, makes a long inspection of the 

 outside of the home and proposes, puny as 

 she is, to introduce her eggs into this cement 

 fortress. Everything is most carefully closed: 

 a layer of rough plaster, at least two-fifths of 

 an inch thick, entirely covers the central ac- 

 cumulation of cells, which are each of them 

 sealed with a thick mortar plug. And it is 

 the honey of these well-guarded chambers 

 that has to be reached by piercing a wall al- 

 most as hard as rock. 



The parasite pluckily sets to; the idler be- 

 comes a glutton for work. Atom by atom, 

 she perforates the general enclosure and 

 scoops out a shaft just sufficient for her pas- 

 sage; she reaches the lid of the cell and 

 gnaws it until the coveted provisions appear 

 in sight. It is a slow and painful process, 

 in which the feeble Stelis wears herself out, 

 for the mortar is much the same as Roman 

 cement in hardness. I find difficulty myself 

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