V'^'-^^'^-] Ddvi;, Xn/i's on Pcirusi/ism. 305 



usually three or four to one ; and instead of a large crop of old 

 bachelors, she goes with all of them." So here again we have 

 polyandry of a pronounced type in conjunction with the parasitic 

 habit. My contention is that the great preponderance of males 

 is at the root of parasitism. If we can find out why the eggs of 

 the Cuckoos and of the Cow-Birds, which make other species 

 hatch and rear their children, produce three or four males to one 

 of the other sex, we shall then be at the root of the matter. 

 Nothing is gained by re-advancing at the present day theories of 

 faulty anatomy as the cause of non-incubation, when these were 

 exploded more than a century ago by old Gilbert White, of 

 Sell)orne. 



Having always considered the subject of parasitism one of 

 tlu' most important — and puzzling — ^with which the ornithologist 

 lias to deal, I felt gratified when fortune threw in my path this 

 spring the compact nest of a Brown-tail {Acanthiza diemenensis), 

 containing two eggs of the builder and one of the Fan-tailed 

 Cuckoo [Cacomantis flahelHformis). With the intention of 

 carrying out a series of observations after hatching had begun, 

 I visited the nest again after the lapse of three days, and found 

 it quite intact, but all the eggs had disappeared, and left not a 

 wrack behind ! The structure was so compact and well hidden, 

 and so close to the ground (within 3 inches), that it is unlikely 

 anyone else would notice it, and a boy would almost certainly 

 have pulled it out of position. It seems probable that either a 

 rat or snake was the culprit ; the locality is quite a " snaky '' 

 one, two having been slain already this season not far away, and 

 a third sighted. Having lately read Dr. Ramsay's remarks (as 

 quoted on p. 570 of Campbell's " Nests and Eggs ") as to the 

 alleged enlargement of entrance of Acanthizas' nests by deposition 

 of Cuckoo's egg, I took careful note of the entrance to the one 

 recently discovered, and certainly could not have judged by its 

 appearance that an egg of the intruder had been placed within. 

 The small circular aperture, protected by projecting eave just 

 abov(\ was an inch in diameter, and Mr. Campbell's remark 

 that " it hardly admits one's finger " was fully justified, for it 

 was with the greatest difficulty that I was able, by insertion of 

 the forefinger, to hook up one egg at the time to the mouth of 

 aperture without disturbing the structure. This was the only 

 possible way to know what eggs were within, for it was an absolute 

 impossibility to look into the nest. Even had it been away from 

 the tangle of grass and small bracken in which it was built, the 

 depth of the structure and the projecting eave (so-called " hood ") 

 over the entrance, quite near the top of ne.st, would have made 

 the interior quite invisible. There was no appearance whatever 

 of the " hood " having been pushed back so as to render the eggs 

 visible, as noted by Dr. Ramsay in the case of Acanthiza pusilla 

 in New South Wales, and which he put to the credit of the 

 intruding Cuckoo (pp. 569-570, Campbell's "Nests and Eggs"). 

 In the case of the 'I'asm.inian nest, tlu^ eave was just as normal 



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