THE ANATOMY OF BIRDS. ^ OOLOGY. 223 



patamen, a peel, rind), or "egg-pod"; it is the final envelope of such a "soft-shelled egi; " 

 as a hen drops when deprived of the lime required to enahle her to secrete a hard shell, hi 

 the nterine dilatation of the oviduct a thick white fluid charged with earthy matter is exuded ; 

 this condenses upon the egg-pod and forms the shell. The coui;)ositiou of this eartli is chieily 

 carbonate of lime (common chalk), with some carbonate of magnesia, and pliosphates of l)otli 

 of these bases — thus like that of bone as to ingredients, but in very dillereut propurtions. The 

 shell does not simply overlie the pod in a distinct sheet, but is intimately coherent, the micro- 

 scopic crystals or other particles of the earthy matter being deposited in the matted fibrous 

 texture of the pod. The connection is must intinuite in fi-esh eggs; after a M-Iiile, layers of the 

 pod separate at the butt of the egg, f<jrming the largo air-space which every (jne lias noticed in 

 that situation. The shell being very porous, readily admits air. Tlie air space enlarges dmiug 

 incubation, and the pod becomes more and more distinct from the shell, whicli lattei- idso 

 increases in porosity and fragility towards "full term." The rough or smooth appearance of an 

 egg-shell, the pores which may be visible to the naked eye, and other physical characters, ai-e 

 due to the impression made upon it hj the lining membrane of the " uterus." The superficial 

 deposit of chalk is so heavy, in some cases, as those of cormorants, etc., that it may be scraped 

 off without interfering with the texturally firm shell-substance underlying. All the coloration 

 of egg-shells, which frequently makes them pretty objects, is simply the deposit of pignu-nt 

 granules in or upon the shell. Such deposit may be perfectly uniform, as it is in the bluisli- 

 green egg of a robin, for instance, but it is oftener spotty — either upon a white or a whole- 

 colored ground. The browns and neutral tints are the usual ccjlurs, particularly a bright 

 reddish-brown; the same, lying in instead of upon the shell, gives the grays, "lilacs," and 

 "lavenders" so well known. In ptarmigan, the pigment is so heavily deposited that tlie 

 egg comes out pasty on the sur'face ; a sign of " fresh paint ! " one must not disregard if lie 

 would not spoil the decoration. 



Ovipositlon. — The energy and rapidity witli which the processes involved in the manu- 

 facture of so complex a product as a bird's egg is now seen to be are extrac_)rdinary. A domestic 

 fowl may lay an egg every day for an indefinite period. It is dif&cidt to say how cpiickly an 

 egg may ripen in the ovary; for, during the activity of that organ, several or many are to be 

 found in all stages of immaturity, and the date of the initial impulse cannot well be deterndued. 

 As there is probably but one egg at a time in the oviduct, the whole process of finishing oS th(; 

 yelk -ball \^'ith its chalaziform, soft albuminous, putaminous, and calcareous envelopes may go 

 on in twenty-four hours, most of which time is consumed in the shell-formation. The number 

 of eggs matured by the human female is or should be thirteen annually ; this is no larg(.' number 

 for many of the gallinaceous and anatine birds to deposit in about as many days. But a 

 probable average number is five or six. Defeat of the procreative instinct from any accident is 

 commonly a stimulation to renewed endeavors to reproduce ; and very many birds rear two or 

 three broods annually, though one clutch of eggs is the rule. Many, such as auks, petrels, and 

 penguins, lay a single egg. Two eggs is the rule in humming-birds and pigeons. Three is 

 normal to guUs and terns, though these often have but two. Four is the rule among the 

 small waders of the limicoline groups. Some of the small Oscines lay over the average, 

 having eight or ten ; among these, the European sparrow. Passer domcslimis, is probably the 

 most prolific. The parasitic cuckoos are said to lay the relatively smallest eggs ; that of the 

 Apertyx is said to be the largest, weighing one fourth as much as the birtl. The usual 

 shape of an egg has given us the common names oval, ovate, and ovoidal, for the well-known 

 figure. Some, as those of owls, woodpeckers, kingfishers, and others, more or less nearly 

 approach a spherical shape. Eggs of grebes, herons, Totipalmate birds and various others 

 are rather elliptical, or equal-ended, and narrow in proportion to their length. Eggs of the 

 limicoline group are generally pyriform, — very broad at one end and narrow at the other. But 



