CHAP. V. 



FUNCTION OF REPRODUCTION. 



269 



lular tissue termed the "nucleus" (fig. 164. a), in- 

 vested by two coats or skins (6), open at their lower 

 extremity, and allowing a portion of the nucleus, called 

 its " apex, " to protrude through them. This open- 

 ing is termed the " fora- 

 men." Shortly afterwards 

 these skins close over the 

 nucleus, and leave only a 

 small orifice to the fora- 

 men (c). The outermost 

 of these skins is termed 

 the " testa" or "primine," .-< 

 and the innermost the 

 " tegmen " or " secun- 

 dine." Sometimes there is only one skin, or more 

 probably the two are so blended together that they are 

 not distinguishable. As the ovule enlarges, the nucleus 

 itself is also found to be a closed sack, of a thick or fleshy 

 consistency ; and within this and towards its apex, an- 

 other small sack or vesicle makes its appearance called the 

 "embryonic sack" (fig.l65. a). The ovule may there- 

 fore generally be considered in its early 165 

 state to be composed of two closed sacks 

 which together constitute the nucleus, 

 and of two open sacks which form its 

 integuments. In some cases the two 

 outer skins appear to be blended to 

 gether, for one only can be seen. The 

 number of sacks which compose the nu- 

 cleus sometimes also amounts to three ; 

 so that the whole number contained in 

 the ovule is as many as five, and these 

 have received the several names of pri- 

 mine, secundine, tercine, quartine, and 

 quintine reckoning from without, inwards. Whilst 

 the enlargement of the ovule proceeds, a change of 

 position also takes place in the relation of its parts, 

 owing to an unequal development of the sides of the 

 primine. The apex, which at first was on the side of 



