620 AVES BIRDS. 



absorption ; and the ovulum, with its cicatricula, is left to be 

 clothed with other investments : but the germinal vesicle is now no 

 longer to be seen ; its delicate covering having been, as Ptirkinje 

 supposes, ruptured by the violence to which it has been subjected. 



(696.) It is during the passage of the ovulum through the canal 

 of the oviduct that it becomes enclosed in the other parts entering 

 into the composition of the egg : these are, the albumen, the 

 chalazas, the membrana putamim's, and the calcareous shell. 



The albumen, or glairy fluid forming the white of the egg, is 

 secreted by the mucous membrane that lines the commencement of 

 the oviduct ; and being laid on, layer upon layer, gradually coats 

 the membrana vitelli. Some of the albumen meanwhile becomes 

 inspissated so as to form an almost invisible membrane, the chalaza, 

 which being twisted by the revolutions of the yolk, as it is pushed 

 forward in the oviduct, is gathered into two delicate and spiral 

 cords (Jig- 285, c, c), whereby the yolk is retained in situ after the 

 egg is completed. 



The ovulum, now covered with a thick coating of albumen, 

 and furnished with the chalaza, at length approaches the terminal 

 extremity of the oviduct, where a more tenacious material is poured 

 out : it is here that the whole becomes encased in a dense mem- 

 brane resembling very thin parchment, called " membrana puta- 

 minis ;" and ultimately, on arriving in the last dilated portion of 

 the canal (Jig. 283, g), the lining membrane of which secretes cre- 

 taceous matter, the shell is formed by the gradual accumulation 

 of extremely minute, polygonal, calcareous particles, so disposed 

 upon the surface of the egg that imperceptible interstices are left 

 between them for the purpose of transpiration. 



Thus, as the oviduct is traced from its infundibular commence- 

 ment, the different portions of it are seen successively to discharge 

 the following functions : the orifice of the infundibulum receives 

 the ovulum from the ovisac ; the succeeding portion, extending 

 nearly three fourths of its entire length, secretes the albumen and 

 the chalazas ; it in the next tract furnishes the membrana putami- 

 nis ; and in the last place, the shell ; after which, the complete 

 egg is expelled through the cloaca. 



(697.) The anatomy of the egg prior to the commencement of 

 incubation is therefore sufficiently simple. Immediately beneath 

 the shell is the membrana putaminis ; which, however, we must 

 here remark consists of two layers ; and at the larger end of the 

 egg these layers separate, leaving a space (Jig. 284, a, 6), called 



