OVUM. 



65 



D 



D. Egg from the lower part of the glandular 

 oviiluct near the isthmus, when the deposit of albu- 

 men is complete; the spiral arrangement of the 

 albumen made manifest by slight coagulation. 



attached to the opposite ends or poles of the 

 yolk by means of a membrane which looks ex- 

 actly like a continuation of the twisted part 

 of these bodies opening or expanded over the 

 surface of the vitelline membrane. These 

 bodies attracted considerable notice from the 

 earlier observers of the structure of the egg, 

 and have had various uses attributed to them ; 

 but, if we may judge from the varieties they 

 are subject to in the fowl and other birds, and 

 their absence in the ova of scaly reptiles 

 (otherwise very similar to those of birds), it 

 would appear that they are only of secondary 

 importance. 



One of the chalazse is directed towards the 

 larger, and the other to the smaller end of the 

 egg, and the latter usually adheres with some 

 firmness to the inside of the shell-membrane, 

 while that of the large end floats more freely. 

 In this manner the yolk moves more freely 

 at the large than at the small end of the 

 egg. The spiral twist is in opposite direc- 

 tions in the two chalazae ; a circumstance 

 depending on the manner of their production, 

 by the gradual deposit of albumen and the 

 spiral motion of the yolk during its descent 

 in the oviduct. The membrane which pro- 

 ceeds from the cbalazas over the surface of 

 the yolk has been called chalaziferous ; and 

 the funnel-shaped dilatation of the chalazae 

 where they join the membrane, has been sup- 

 posed to be the opening of a tube passing 

 through these bodies, and serving as a conduit 

 from the white to the yolk ; but entirely 

 without reason. The chalaziferous membrane 

 and innermost twisted part of the chalazoe 

 are, in fact, nothing more than the first- 

 deposited and densest parts of the albumen ; 

 nor is any importance to be attributed to a 

 curved line or fold of the membrane which is 

 often seen stretching over the yolk between 

 the adhering parts of the opposite chalazae. 



The fact of the upturning of the side of the 

 yolk which bears the cicatricula has already 

 been adverted to, as well as the supposition that 

 Snpp. 



the clialazne may be the means of securing 

 this position ; but, although it is well ascer- 

 tained that these bodies control, in various 

 directions, the motions of the yolk, they can- 

 not be the cause of the upturning of the cica- 

 tricula ; as this is secured by the difference 

 of specific gravity in the upper and lower 

 parts of the yolk. The true action of the 

 chalazae is to limit the motions of the yolk in 

 the long axis of the egg, and control the rota- 

 tion during a certain time ; but in incubation 

 the relations of the chalazae, white, and yolk 

 are very soon changed ; and, in the progress 

 of these changes, the remains of the denser 

 white are collected at the lower part of the 

 egg. If a fresh egg be turned round on its long 

 axis, the cicatricula will keep its position up- 

 wards for one turn or a little more, and then, 

 by the twisting of the chalazas, the yolk is 

 carried completely round, and balances itself 

 again with the cicatricula uppermost in its 

 new position. 



The accessory parts of the egg, now de- 

 scribed, are formed round the yolk or ovarian 

 egg during its descent through the oviduct ; and 

 as they may be regarded as only indirectly 

 connected with the functions of the true ovu- 

 lum in their relation to embryonic develop- 

 ment, it may be best to complete their history 

 at this place by stating what has been ob- 

 served as to their formation, referring for this 

 to the researches of Purkinje, Coste, and 

 others, which I have confirmed in most parti- 

 culars by the examination of a considerable 

 number of fowls during the process. 



Formation of the external or accessory parts 

 of the bird's egg. These parts are produced 

 with much greater rapidity than those of the 

 ovulum. Many fowls lay an egg every twenty- 

 four hours for a part of the season, while 

 others lay only every second day, or two or 

 three days in succession, generally at a later 

 hour on each successive day, and then intermit 

 for a day ; other fowls lay regularly nearly 

 every thirty-six hours. There is probably some 

 difference in the rapidity of the descent of 

 the egg, or at least in the length of time it 

 remains in particular parts of the oviduct, in 

 these various cases ; but in general the whole 

 passage of the egg, from the time of the re- 

 ception of the yolk by the infundibulum to its 

 being laid, occupies about twenty-four hours. 

 If a fowl which is laying only every second 

 day, be killed and opened from seventeen to 

 twenty hours, or if one which is laying daily 

 be opened from three to six hours after the last 

 egg was deposited, one of the ovarian capsules 

 will sometimes be found completely enveloped 

 by the infundibulum of the oviduct, which is 

 thus in the act of receiving the ovulum or j'olk 

 about to be discharged by the cleaving of the 

 capsule along the stigmatic band.* The infun- 

 dibulum is contracted round the neck or pedi- 

 cle of the ovarian capsule, so that the whole is 

 embraced by it with moderate firmness, and 

 the yolk thus usually passes securely into the 



* See a later section for an account of the circum- 

 stances which influence the discharge of the ovarian 

 ovula. 



