OVUM. 



67 



Although it can scarcely be doubted that 

 the chalazae are produced during the de- 

 scent of the egg, while the albumen is being 

 deposited, it is worthy of remark, that the 

 twisted structure of these bodies is usually 

 not to be seen till after the shell has begun 

 to be formed * ; but it is very probable that 



Fig. 48. 



Position of the egg in the oviduct as it descends. 



A portion of the oviduct near the lower end 

 opened, taken from a fowl killed three and a half 

 hours after the last egg was laid. The greater part 

 of the albumen has been deposited, and the egg has 

 assumed its peculiar form, the small end of the oval 

 advancing first; the cicatricula placed on the side 

 of the yolk. 



this may depend on their not having pre- 

 viously acquired sufficient opacity or conden- 

 sation to render their tortuous structure ob- 

 vious. Indeed, Von Baer has observed them 

 to make their appearance by increase of their 

 opacity from exposure while under actual 

 observation. 



It has been ascertained by experimental 

 observation that the membrane of the shell 

 is formed in the narrow part of the oviduct, 

 termed the isthmus, which intervenes between 

 the albuminiferous part and the uterine dila- 

 tation. It consists, no doubt, in the fibrillation 

 of consolidated albumen, or some analogous 

 substance, which must take place with great 



within the white, and that it is only towards the 

 end of the period of its passing through the oviduct 

 that a liquefaction of the albumen, which then occurs, 

 permits this rotation : but I think it doubtful that 

 the adhesion between the surface of the yolk and 

 deeper albumen is so great as to prevent the degree 

 of rotation above referred to. 



* Von Baer, Uber Entwick. p. 31. 



rapidity ; but we are not yet sufficiently ac- 

 quainted with the nature of this process, for 

 the phenomena of the solidification and fi- 

 brillar organisation have not been minutely ex- 

 amined, nor has any difference yet been ascer- 

 tained between the substance secreted in the 

 isthmus, which undergoes the fibrillation with- 

 out calcification, and that of the uterine dila- 

 tation, which seems to have no such tendency, 

 remaining amorphous or cellular, and having 

 very soon a deposit of calcareous matter 

 formed in it. 



By the time the egg arrives in the uterus, 

 it has acquired its peculiar oval form, the 

 small end pointing downwards in the oviduct. 

 The cause of this form, which is already ap- 

 parent in the white previous to the formation 

 of the shell, is somewhat obscure, on account 

 of the complexity of the mechanical condi- 

 tions influencing the egg in its passage. It 

 may probably depend on the circumstance 

 that the soft mass dilates the oviduct more 

 gradually as it insinuates itself between its 

 coats, in being propelled onwards, while the 

 part of the duct through which it has passed 

 contracts more abruptly and firmly in conse- 

 quence of the stimulus of distension to which 

 it has been subjected. But the variety of 

 forms which occurs in the eggs of different 

 birds and other animals must not be for- 

 gotten, as indicating that the peculiarity of a 

 lesser and greater end is not essential, and 

 may depend on very slight or transient cir- 

 cumstances. Perhaps, the greater density of 

 the albumen, secreted over the end which 

 advances first in the oviduct, may also have 

 some effect in giving this part the smaller 

 volume. It certainly seems remarkable that 

 the ends of the egg should be moulded into 

 so smooth and rounded a surface as that of 

 the membrane and shell by a tubular organ. 

 In some rare instances, however, I have ob- 

 served irregularities of form at the extremities 

 of the egg, indicating an imperfect contraction 

 of the oviduct during the passage. 



The egg remains a much longer time (from 

 twelve to eighteen or more hours) in the 

 uterine dilatation of the oviduct during the 

 formation of the shell. The mucous mem- 

 brane of this part differs in structure consi- 

 derably from the rest: it presents over its 

 whole extent large villous-like processes, or 

 short folds, of a flattened form, containing small 

 follicular glands, from which the substance of 

 the shell is secreted. As soon as the egg 

 enters this part of the passage a thickish 

 white fluid is poured out from the membrane, 

 which speedily coagulates on the surface of 

 the membrane lining the shell, and very soon 

 we can perceive with the microscope small 

 heaps or united groups of particles somewhat 

 of a crystalline appearance, but in reality cal- 

 cified blastema studded over the whole surface. 

 These are the calcareous particles of the shell, 

 which are deposited in a delicate matrix of 

 animal tissue of a large cellular structure. 

 The deposit goes on rapidly increasing: at 

 first the shell is soft, it remains friable for 

 a considerable time, and, subsequently, it 



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