DESCRIPTION OP THE SEXUAL PRODUCTS. 



17 



the ovary and is taken up by the oviduct, several secondary en- 

 velopes derived from the wall of the oviduct, viz., the white of the 

 egg, or the albumen, the shell-membrane, and the calcareous shell. 

 Each of these parts is formed in a special region of the Hen's oviduct. 

 The latter is divided into four regions : (1) A narrow ciliated 

 initial part, into which the liberated egg is received, and where it 

 is fertilised by the spermatozoa already accumulated there ; (2) a 



y-y- 



w.y. 



eh.!. 



Fig. 8. Diagrammatic longitudinal section of an unincubated Hen's egg, after ALLEN THOMSON. 

 (Somewhat altered.) 



b.l. Germ-disc ; w.y. white yolk, which consists of a central flask -shaped mass and a number of 

 concentric layers surrounding the yellow yolk (y.y.) ; v.t. vitelline membrane ; x. a somewhat 

 fluid albuminous layer, which immediately envelopes the yolk ; w. albumen composed of 

 alternating layers of more and less fluid portions ; ch.l. chalazse ; a.ch. air chamber at the 

 blunt end of the egg simply a space between the two layers of the shell-membrane ; i.t.m. 

 inner, s.m. outer layer of the shell-membrane ; s. shell. 



glandular region, covered with longitudinal furrows, from which 

 the albumen is secreted and spread around the yolk in a thick layer ; 

 (3) a somewhat enlarged part, covered with small villi, the cells 

 of which secrete calcareous salts, and thus cause the formation of 

 the shell ; (4) a short narrower region, through which the egg 

 passes rapidly, and without undergoing any further change, when 

 being deposited. 



The envelopes furnished in succession by the oviduct have the 

 following composition : 



The white of the egg, or albumen (w), is a mixture of several 

 materials : according to chemical analyses, it contains 12% albumen, 



