THE ANATOMY OF BIRDS. — OOLOGY. 233 



to bo incubated and hatdiod simultaneously. It is not so unusual among American cuckoos 

 as generally supposed. The degree of d(!velopmeut to which biids attain in the egg has been 

 already discussed (p. 91). They break the shell by pecking at it, and struggling; for tlie 

 former operation the bill is often tempered at the tip by a hard knob which 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 the extraordinary taste and ability many birds dis- 

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

 delightful departments of ornithology, called caliology (Gr. KoKia, kalia, 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 

 (Ploceidce) probably taking the lead. The male sometimes constructs his own "nest" apart 

 from that in which the female incubates. "Certain conirostral Cawtores still practise in the 

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

 nesting-place. The satin bower-bird (Ftilonorhynchus holosericeus) , and the pink-necked 

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

 avenues, over-arched by l(»ng twigs or grass-stems, the entry and exit of which are adorned by 

 pearly shells, bright-colored feathers, bleached bones, and other decorative 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 ncited at p. 004. "Edible birds'- 

 uests," constructed by swifts of the genus Collocalia, c(jnsist chieHy of inspissated saliva. 

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

 its own body, tlie 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 arl»itrary and artilicinl. 

 They are an attempt to take the student by a "short cut" to the name and position in 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"; n(d)ody can be 

 smuggled into sound erudition, 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 bird, at any rate. That is what the ])receding 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 which can by any possibility be characterized intelligil)ly in 

 a line of type. I have probably simplified and expedited matters by ))reparing on the same 

 plan Keys to the Orders and Sub-orders, and to the Fainilics. Tiicn in 

 work, under each head, further analyses are givfai when such seems to 

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

 their genera. These ulterior analyses are for the most part rather natun 

 though I never liesitate to seize ujion awy character that may furnish the desi 

 ficati<jn. 



The artificial Keys immediately ftdlowing will take the student to i\\c families, with refer- 

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



