222 



GENEBAL ORNITHOLOGY. 



which gets hold of the ovum to drag it down to the common lot of mortals from its high ovarian 

 birth. The infundibulnm receives from the mesentery a delicate tunic of unstriped muscular 

 fibres, which are so disposed as to dilate that orifice for the reception of the ovum ; and during 

 the venereal orgasm the mouth of the tube is supposed to seize upon the ripest egg. The 

 actual anatomy of the arrangement, and the whole operation, is strangely suggestive of one of 

 the oldest myths respecting the serpent which bore the egg of the world in its jaws. The 

 mucous lining of the oviduct consists of a layer of ciliated epithelium ; the membrane has a 

 different character in successive portions of its extent. Above, when the tube is not distended 

 with its burthen, the lining is thrown into lengthwise folds, which lower down become spirally 

 disposed, and then longitudinal again before they cease. This rugous portion of the tube is 

 beset with mucous follicles, which secrete "the white." The oviduct, after contracting at a 

 point called the isthmus, enlarges to a calibre sufficient to accommodate the egg in its shell; 

 for this is the shell-forming part, homologous with the mammalian uterus (a sinister semi -uterus 

 at least), lined with large villi, and beset with the follicles whose secretions calcify the egg-sheU, 

 and decorate it with pigment. The rest of the tube is vaginal, being merely the passage-way 

 by which the perfected ovum is discharged into the cloaca, to be expelled per anum. The 

 musoiilar walls of the oviduct consist of both circular and longitudinal unstriped fibres, like 

 those of intestine, — the latter especially in upper portions and at the infundibulum, the former 

 more conspicuously below, where they form a sort of os tinea at the bottora of the calcific 

 portion, and a kind of sphmcter vagmcs at the end of the tube. A recognizable cUtoris is 



developed in many birds. 



The deposition of the white and of the shell 

 remains to be noticed. The first deposit upon 

 the yelk-ball consists of a layer of dense and 

 somewhat tenacious albumen, called the chala- 

 eiferous membrane (Gr. xa'^^afa, chalaza, a tu- 

 bercle, and Lat. fero, I bear). As the egg is 

 urged along by the peristaltic action of the 

 tube, it acquires a rotation about the axis of the 

 tube ; the successive layers of soft albumen it 

 receives are deposited somewhat spirally; and 

 the chalaziferous membrane is drawn out into 

 Fio. 110. —Hen's egg, nat. size, in section; from threads at opposite poles of the egg. These 

 Owen, after A. Thompson. A, oioatrlcle or " tread," threads, which become twisted in opposite direc- 

 with its nucleus, of white germ-yelk, floating on surface . . . '■ '^ 



of pale thin nutritive yelk, leading to central yelk- tions during the rotation of the egg, are called 

 cavity, a;; a, the yeUow yelk-ball, deposited in the sue- chalaza ; they are the " strings," rather un- 

 cessive layers, forming a set of Aa/ongs, and enveloped _ - ., . ri-i^ 



in the chalaziferous membrane which is spun out. at pleasantly evident m a soft boiled egg, but serve 

 opposite poles into the twisted strings, chalazse, c, c ; the important office of mooring and steadying the 

 6, i', successive investments of softer white albumen ; n • ^i r -i -^ i ^ . ti 



d, membrana putaminis, the "soft shell" or egg-pod, yelk m the sea of white by adhesions eventually 

 between layers of which at the great end of the egg is contracted with the membrane which immedi- 

 eairsp^,/^, e, e e . ately lines the shell. They are also intrusted 



with the duty of ballasting, or keeping the yelk right side up. For there is a "right side" 

 to the yelk-ball, being that on which floats the cicatride, or "tread." This side is also the 

 lightest, the white yelk being less dense than the yellow ; and the chalaza are attached a little 

 below the central axis. The result is, that if a fresh egg be slowly rotated on its long axis, 

 the tread vriU rise by turning of the yelk-ball in the opposite direction, tUl, held by the twisting 

 of the chalazae, it can go no farther ; when, the rotation being continued, the tread is earned 

 under and up again on the other side, resuming its superior position as before. After all the 

 spiral layers of soft white are laid on, a final covering of dense albumen is deposited at the 

 isthinic part of the oviduct. This forms a tough tunic called the membrana putaminis (Lat. 



