THE ANATOMY OF BIBBS. — OOLOGY. 227 



to be incubated and hatched simultaneously. It is not so unusual among American cuckoos 

 as generally supposed. The degree of development to which birds; attain in the egg has been 

 already discussed (p. 8S). They break the shell by pecking at it, and strugghng ; for the 

 former operaticm the biU is often tempered at the tip by a hard knob ivliich is afterward ab- 

 sorbed. The necessity of providing a receptacle for eggs, in which they may be incubated, 

 results in nidification or nest-building ; and tlie extraordinary taste and abihty many birds dis- 

 play iu this matter, as well as the wide range of their habitudes, furnishes one of the most 

 delightful departments of ornithology, called calioloyy (Gr. Kokia, kiilia, a bird's nest; see 

 p. 54, note). Many birds burrow in the ground; others in trees; the most beautiful and 

 elaborate nests are furnished by various members of the Oscines, the weaver-birds of Africa 

 {Ploceidtc) probably taking the lead. The male sometimes constructs his own "nest" apart 

 from that iu which the female incubates. "Certain couirostral CfOitores still practise in the 

 undisturbed wilds of Australia the formation of marriage-bowers distinct from the later-formed 

 nesting-place. The satin bower-bird (Ptilonorhijnchits liolosericens), and the piuk-ueeked 

 bower-bird (Chlamijdodera maculata) , arc remarkable for their construction on the ground of 

 avenues, over-arched by long twigs or grass-stems, the entry and exit of wliich are adorned by 

 pearly shells, bright-colored feathers, bleached boues, and tither decorati\-e materials, which are 

 brought in profusion by the male, and variously arranged to attract, as it would seem, the 

 female by the show of a handsome establishment" (Owen). The extraordinary nests of the 

 Crotophaga, used in common by a colony of the birds, are noted at p. 471. " Edible birds'- 

 nests," constructed by swifts of the genus CoUocalia, consist chiefly of inspissated saliva. 

 Perhaps the most remarkable of all the receptacles of eggs is that which the penguin makes of 

 its own body, the egg being carried in a sort of pouch formed by the integument of the belly, 

 something like that of a marsupial mammal. 



§ 5. DIRECTIONS FOR USING THE ARTIFICIAL KEYS. 



These "Keys" differ from natural analyses in being wholly arbitrary and artificial. 

 They are an attempt to take the student by a "short cut " to the name and position iu the orni- 

 thological system of any specimen of a North American bird he may have in hand and desire to 

 identify. The plan has been much used in Botany, though seldom if ever employed for a 

 whole Fauna, before the original edition of this work. It will serve a good purpose, rightly 

 used; but it must be remembered there is no "royal road to learning"; nobody can be 

 smuggled into sound eruditi<ju, either. Nor must too much be expected of me here ; I can 

 take the student nowhere until he has learned the difference between the head and the tail of 

 a bu-d, at any rate. That is what the preceding pages undertake to teach ; but, until such 

 technicalities have been mastered, progress in ornithology is out of the question. 



The original " Key to the Genera" proved scarcely so satisfactory as I hoped it would be. 

 It undertook too much, to conduct the student at once down to the intricacies of the very 

 many modern genera, not all of wlii(-h can by any possibihty be characterized inteUigibly in 

 a hue of type. I have probably simplified and expedited matters by preparing on the same 

 plan Keys to the Orders and Sub-orders, and to the Families. Then in the body of the 



work, under each head, further analyses are given when sucli seems to be required of 



families under their orders or sub-orders, of genera under their families, and of species under 

 their genera. These ulterior analyses are for the most part rather natural than artificial 

 though I never hesitate to seize upon any character that may furnish the desired clue to identi- 

 fication. 



The artificial Keys immediately foUowing will take the student to the families, with refer- 

 ence to the page of the work where such groups come : on turning to which, further analyses 



