155 



external layer can only with difficulty be made 

 out (Fig. 39). 



The nucleus of the ovum undergoes very pro- 

 nounced changes. It appears as an irregular 

 mass, staining uniformly with nuclear stains. 

 This mass becomes more and more distorted and 

 broken up, and eventually disappears. It may 

 frequently, however, be seen as irregular masses 

 of staining material even in the mature egg. A 

 portion of the nucleus is seen very early to be 

 separated off from the rest, often surrounded by 

 the latter. This portion (female pronucleus) is 

 small and difficult to detect in sections in the 

 more mature ovum. As the ovum increases still 

 more rapidly in bulk, the nurse cells become 

 crowded into the distal portion of the follicle and 

 eventually disappear, so that, in the mature egg, 

 no trace of them is to be seen. The epithelial 

 layer surrounding the follicle becomes much 

 flattened, and forms eventually a covering to the 

 egg (chorion). The outer portion of this covering 

 (exochorion) is transparent, and marked with 

 oblique parallel markings. Over the proximal 

 end, i.e., the end lying towards the ovarian tube, 

 the chorion forms a globular mass ornamented 

 with rows of pits. This is the micropylar appara- 

 tus through which the spermatozoa penetrate the 

 ovum. 



Frequently in Anophelines a large portion or 

 the whole of the adult ovum consists of a mass of 

 sporozoa. These consist of numerous small cysts, 

 each containing eight round or crescent-shaped 

 bodies,each with a central chromatin spot (Fig. 40). 



The ovarian tube arises in the centre of the 

 ovary, and receives on all sides the follicular 



