66 



OVUM. 



oviduct; but it occasionally happens that 

 capsules burst without being so embraced, or 

 that the process is disturbed, and the sub- 

 stance of the yolk falling into the abdominal 

 cavity of the fowl either produces serious 

 injury by peritoneal inflammation, or may be 

 gradually removed by absorption. 



The yolk enters the infundibulum, with its 

 long axis corresponding to that of the oviduct, 

 consequently with the cicatricula on its side, 

 which we shall find to be its position also in 

 the completed egg. 



The passage of the yolk through the first 

 two-thirds of the length of the oviduct, in 

 which part the albumen is deposited, is very 

 rapid, scarcely occupying more than three 

 hours, according to Coste*, before it arrives 

 in the narrow or constricted part of a more 

 limited extent (isthmus), in which the mem- 

 brane of the shell is formed. About three hours 

 more suffice for this process, and the ovum then 

 enters the dilated portion, which has been 

 called uterus, in which the substance of the 

 shell is deposited and gradually consolidated 

 on its surface. 



The albumen begins to be deposited round 

 the yolk, immediately upon the entrance of 

 the latter into the oviduct j at first in a thin 

 layer, immediately investing the yolk, which 

 subsequently becomes condensed into the 

 chalaziferous membrane, and in two long 

 narrow portions extending before and behind 

 the yolk from its poles, which portions ot 

 albumen are at first straight and simple, but 

 afterwards become twisted and form the 

 chalazas. ( See fig. 46, A.) 



In the next part of the albumimferous part 

 of the oviduct, in which the glandular struc- 

 ture is most fully developed, the albumen is 

 deposited in much greater quantity round the 

 yolk and chalaza3, not following the form ot 

 the latter, and thus soon gives to the whole 

 the oval shape which belongs to the egg; and 

 we then recognise, previous to the formation 

 of the shell or its lining membrane, that the 

 narrower end of the oval is placed down- 

 wards, or advances first in the oviduct. 



During the passage of the egg, and the 

 formation of the albumen, membrane, and 

 shell, a greatly increased determination of 

 blood is observed in the vessels of the se- 

 veral parts of the oviduct. (See j%. 47.) 



The formation of the accessory parts ot the 

 eg( r appears to proceed nearly in the same 

 manner in the scaly reptiles as in birds. The 

 accompanying figure, borrowed from the 

 article Reptilia, is illustrative of the mam 

 features of the process. 



The advancing motion of the egg qf the fowl 

 is caused by the peristaltic action of the muscu- 

 lar coat of the oviduct, which may be easily seen 

 in any laying fowl opened immediately after 

 death. The egg does not descend, however, 

 in a straight line, but in a spiral direction, 

 corresponding with that of the ridges of 

 glands with which the mucous membrane 

 of the oviduct is beset. Two peculiarities 

 in the structure of the albuminous part ^ of 

 the egg result from this spiral motion viz., 



* Hist. gn. et partic. du De'vel. &c. 



fig. 47. 



Descent of the egg in the oviduct of the Tortoise 



(after Bojanus). 



A. Infundibular opening of the oviduct; n, o,p, 

 canal of the oviduct laid open; s, *, ovum opened, 

 showing the yolk, albumen and shell; B, allantoid 

 bladder ; F, oviduct ; c, D, kidney ; E, ureter ; m, 

 termination of the opposite oviduct, 

 the spiral laminated form of the outer layers 

 of albumen, and the marked tortuosity ot t 

 chalazse. It is easy to understand how t 

 spiral form is given to the deposit ot the 

 layers of albumen. The cause of the pecu- 

 liar manner in which the chalazae are twisted 

 is not so immediately apparent . it may b 

 explained as follows. As already remarked, 

 the spiral twist is in an opposite direction m 

 the two chalazse ; one end of each ot these 

 cords must, therefore, have remained in a 

 state of rest as compared with the other. 

 Either, it may be supposed, the farther ends 

 of the two chalazre extending into the ovi- 

 duct before and behind the descending yolk, 

 remain comparatively at rest, while that body 

 with the albumen forming round it being 

 closely embraced by the oviduct has the ro- 

 tary motion impressed upon it ; or, as is more 

 probable, when the chalaza3 become attached 

 to and involved in the deposited albumen, 

 their outer ends move with it, while the yolk 

 within, to which the inner ends of the chalazae 

 are fixed, does not rotate in the same degree; 

 a circumstance to which it is possible the dis- 

 position of the side on which the cicatricula 

 is placed to remain uppermost may m some 

 degree contribute; and thus the yolk not turn- 

 in^ so rapidly, or so often as the white, the 

 chalazse are twisted upon their roots attached 

 to the surface of the yolk.* 



* It ought to be observed, however, that according 

 to Coste, the yolk does not at first rotate freely 



