STRUCTURE OF THE OVARY. 



849 



Fig. (538. 



Section of a cat's ovary. The place of attachment 



or hiluni is below. On the left is a corpus luteum. 



to the view that the spermatozoa are, in part at least, formed within round cells, 

 by a process of endogenous development. 



According to Benda and v. Ebner, the spermatoblasts are formed by the coalescence (copula- 

 tion) of a group of seminal cells with the lower part of the foot-plate and stalk of the spermato- 

 blasts. Each seminal cell forms from 

 its nucleus the head, and from its pro- 

 toplasm the tail of a spermatozoon. 

 For the complete formation of these 

 parts, there must be a coalescence of 

 the seminal cells with the spermato- 

 blasts. 



Shape. The spermatozoa of most 

 animals are like cilia with larger or 

 smaller heads. The head is elliptical 

 (mammals), or pear-shaped (mammals), 

 or cylindrical (birds, amphibians, fish), 

 or cork-screw (singing birds, paludina), 

 or merely like hairs (insects fig. 636). 

 Immobile seminal cells, quite different 

 from the ordinary forms, occur in 

 myriapoda and the oyster. 



433. THE OVARY OVUM 

 UTERUS. [Structure of the Ovary. 



The ovary consists of a connective- 

 tissue framework, with blood-vessels, 

 nerves, lymphatics, and numerous non-striped muscular fibres. The ova are embedded in this 

 matrix (fig. 638). The surface of the ovary is covered with a layer of columnar epithelium 

 (fig. 639, e), the remains of the* 

 germ- epithelium. The most 

 superficial layer is called the 

 albuginea ; it does not contain 

 any ova. Below it is the corti- 

 cal layer of Schron, which 

 contains the smallest Graafian 

 follicles ( T ^ T inch fig. 638), 

 while deeper down are the 

 larger follicles (J-$ to yfo inch). 

 There are 40,000 to 70,000 

 follicles in the ovary of a female 

 infant. Each ovum lies within 

 its follicle or Graafian vesicle. ] 

 Structure of an Ovum. 

 The human ovum (O. E. v. 

 Boer, 1827) is 0*18 to 0'2 mm. 

 [x^-g- in.] in diameter, and is 

 a spherical cellular body with 

 a thick, solid, elastic envelope, 

 the zona pellucida, with 

 radiating striae (fig. 640). The 

 zona pellucida encloses the 

 cell-contents represented by 

 the protoplasmic, granular, 

 contractile vitellus or yelk, Section of an ovary, 



which in turn contains the 2 > 2 > raiddle Slz ed, and 3, 3, smaller sized follicles ; 0, ovum 

 eccentrically placed spherical within a Graafian follicle ; v, v, blood-vessels of the stroma ; 

 nucleus or germinal vesicle 9> cells of the membrana granulosa. 

 (40-50 fi Purkinje, 1825 ; Coste, 1834). The germinal vesicle contains the 

 or germinal spot (5-7 /j. E. Wagner, 1835). The chemical composition is given in 

 [Ovum. Cell. 



Zona pellucida corresponds to the Cell-wall. 



Vitellus ,, ,, Cell-contents. 



Germinal vesicle ,, ,, Nucleus. 



Germinal spot ,, ,, Nucleolus.] 



[This arrangement shows the corresponding parts in a cell and the ovum, and in fact the 

 ovum represents a typical cell. ] 



3h 



Fig. 639. . 

 germ-epithelium; 1, large sized follicles; 



nucleolus 

 232. 



