VIPOSITOR. 



[ 565 ] 



OVULE. 



capes surrounded by the cells of the proli- 

 gerous disk and the adjacent part of the 

 epithelium ; the inner surface then becomes 

 wrinkled, and gives off flesh}' processes 

 which become yellowish, and form the cor- 

 pora lutea. 



In those animals in which the amount of 

 stroma present is small in proportion to the 

 size of the vesicles, the ovaries have a race- 

 mose appearance. 



In many of the lower animals the ovaries 

 are tubular, the ova lying closely packed 

 within them. 



BIBL. Kb'lliker, Mik. An. ii. ; Siebold, 

 Vergl. An. ; Todd's Cyclop. An. ; Waldeyer, 

 Strieker's Hist.] Baifour, Gomp. Embryol. 

 1880. 



OVIPOSITOR See INSECTS, p. 433. 



OVULE or OV'ULUM. The name ap- 

 plied to the rudiment of the seed of Flower- 

 ing Plants, produced in the ovary or ger- 

 men during the development of the flower, 

 fertilized by the pollen-grains when com- 

 plete ; and afterwards converted into a SEED 

 by the development of the EMBRYO and 

 other secondary structures during the con- 

 version of the ovary into the fruit. For the 

 general conditions of the ovules in ovaries, 

 reference must be made to botanical works. 

 The ovules make their appearance upon the 

 placenta as cellular papillae rising up from 

 its surface, and are at first simple ; this first 

 development, the main feature of the organ, 

 is called the nucleus (figs. 540-542). In 



Fig. 540. 



Fig. 541. 



Atropous ovules. 

 Fig. 540. Young ovule of Chelidonium. , nucleus; 



ch, chalaza. 

 Fig. 541. Young ovule of mistletoe, consisting of a 



nucleus only. 



rare cases this remains naked ; but in most 

 instances one or two coats are produced, 

 arising as circular folds near the base, and 

 gradually growing up over the nucleus 

 (fig. 542), leaving only a small hole or pas- 

 sage at the apex, leading down to the point 

 of the nucleus. When two coats are 

 formed (fig. 543), the inner appears first; 

 the outer originates later and grows up over 



the inner, and it is generally thicker and 

 more developed. The inner is the secundine 

 of Mirbel, the outer the primine (figs. 543, 

 544, 547, S, P). German writers reverse 



. 543. 



End 



- P 



Atropous ovules. 



Fig. 542. Young ovule of walnut, consisting of a nucleus 

 2f, with a single coat S ; End, the endostome 

 or micropyle. 



Fig. 543. Young ovule of Pplygonum. F, funiculus; 

 P, primine (of Mirbel) ; S, secundine; Ex, 

 exostome ; End, endostome. 

 Magnified 40 diameters. 



these names, resting on the true order of 

 development. Some term them the integu- 

 mentum, internum and externum. The inner 

 is the tegmen, the outer the testa of Brown. 

 The passage at the apex, leading to the nu- 

 cleus, is called the micropyle ; sometimes the 

 orifice in the outer coat is distinguished 

 from that in the inner coat, and they are 

 termed respectively exostome and endostome 

 (fig. 547). While the nucleus and coats 

 are becoming perfected, one of the cells 

 situated near the apex of the nucleus takes 



Fig. 544. 



^^- 



Sections of atropous ovule of Polygonum. 



P, primine ; S, secundine ; N, nucleus ; SE, embryo- 

 sac : V.e, PI, nascent embryo. 



Magnified 20 diameters. 



on a peculiar character, becoming more de- 

 veloped than the rest, and often causing the 

 absorption of part, or sometimes the whole, 

 of the tissue of the nucleus ; it appears at 

 length as a large sac occupying the centre of 

 the ovule j this is the embryo-sac (fig. 544). 

 The base of the ovule is pushed up from 

 the surface of the placenta during its deve- 

 lopment so as to appear at length sup- 

 ported on a stalk of variable length ; this is 



