34 General Part. 



called tlie ovary. Its structure differs largely in different animals j 

 it always^ however, contains egg-cells in different stages of develop 

 mentj held together by connective tissue. Frequently the ovary is a 

 hollow, glandular organ which is continued into a tubular oviduct. 

 The ripe ova break loose, fall into the cavity of the ovary, and reach 

 the exterior through the oviduct. In other cases it is a compact 

 organ, attached to the wall of the body cavity; the ova fall 

 into the body cavity and pass out by a tube opening into it at 

 one end and to the exterior at the other. Before leaving the body of 

 the parent, the ovum is often enveloped in different hard or soft 

 coverings (albumen, shell), secreted by glands opening into the 

 oviduct. Saccular evaginations are frequently present for storing the 

 spermatozoa received during coitus (receptacula seminis). Further, 

 part of the oviduct is often expanded to form a uterus in which the 

 eggs may be retained for some time, often until they have undergone 

 a part of their development. 



Wten the ovum has attained its full size, the nucleus moves to the surface, 

 and divides into two. The protoplasm undergoes corresponding division, but 

 into two unequal pajts, so that before separation, one part looks like a 

 little bud of the larger egg-cell : a second small cell is constricted off in 



Fig. 27. Diagram of the formation of polar 

 bodies. In the left flgnre the first, in the middle 

 the second, polar body is shown in process of 

 formation ; the right figure shows the ripe ovum 

 with both. 



the same way; and as soon as these polar or directive bodies are 

 formed, the ovum is mature and ready for fertilisation. The first polar body 

 may sometimes divide again, so that altogether three are present. They are 

 formed whilst the ovum is still in the ovary, or soon after its liberation ; later, 

 they atrophy. 



The spermatozoa are formed in the testis, which contains 

 sperm-cells in diff'erent stages of development. The testis even more 

 often than the ovary has a glandular structure, and the spermatozoa 

 usually pass out by a duct, the s e m i n a 1 duct or vas deferens, 

 with which it is in direct connection. Organs for the transmission of 

 the spermatozoa into the female apparatus are often present at the 

 external opening of the duct (oopulatory organ, penis). Sometimes 

 the genital products which pass from the male to the female are 

 enveloped in a sheath formed by the hardened secretion of certain 

 glands opening into the vas deferens. Such a mass is called a 

 spermatophore (Cephalopoda) . 



In most species, some individuals give rise to ova only (females), 

 and others to spermatozoa (males). There are, however, many 

 animals, e.g., many Gastropods, which produce both : these are 

 known as hermaphrodites. In this case there is either a 

 specialised ovary (or more than one) and a specialised testis in .the 



