or some of the moss plants, both kinds of gametes are 

 produced near together on the same plant. 



In the fresh-water hydra, described in Chapter Four as 

 producing by buds, reproduction by gametes also occurs. 

 In this little animal eggs and sperms are formed at 

 somewhat different parts of the body, and each hydra is, 

 so to speak, one sex at one point and the other sex at 

 another point. 



This state of having both sexes in one organism is 

 known as hermaphroditism. In addition to the instances 

 mentioned above, it occurs regularly in many of the 

 worms, in snails, oysters, etc. Hermaphroditism may 

 occur in occasional individuals of higher species, even 

 among the vertebrates. 



3. The Organs That Produce Eggs and Sperms. 

 Although a plant or an animal may produce both male 

 and female offspring at the' same time, it is usually true 

 that such a parent has special and different organs for 

 each. Often they are definitely located at different parts 

 of the body. 



The organs that produce the gametes are quite differently 

 named in different organisms. Generally among animals 

 the male organ, which produces sperms, is known as a 

 spermary or testis, and female organ is called an ovary. 

 Among plants the organ that produces sperms is called 

 an antheridium. The female organ in which the egg is 

 produced is called, in different groups, oogonium or 

 archegonium. 



Where gametes are alike, there is only one kind of 

 organ to produce them. There is no reason why there 

 should be more. When the gametes become different, 

 the sex of the cells seems to be stamped on the organs 

 that produce them. An experienced biologist can usually 

 tell which sex an organ represents, even though he has 

 never seen the organism before. The sex quality of the 

 organ becomes as marked as that of the gametes 

 themselves. The gametes are specialized. The organ 

 that produces them becomes equally so. 



4. Specialization of the Parents. Where the gametes 

 are alike, there is no difference in the organs that produce 

 them, and the parents are all alike. But a step higher up 

 we also find different kinds of gametes, produced in 

 different types of organs, but all in one kind of parent. 

 One of the very best illustrations of this in the animal 

 kingdom is the common earthworm. In certain segments 

 of its body-cavity it produces sperms; in other segments 

 it is producing eggs. Each earthworm must perform all 

 the duties of father and mother. 



But in the very same group of worms, in some of the 

 marine forms, we find a surprising difference. In these 

 one animal produces one or the other kind of gametes; 

 not both. If one segment of these worms produces 

 sperms, all the segments produce sperms, and the whole 

 animal is- a male. Other worms produce eggs only. These 

 eggs and sperms from different animals must unite. Here 

 we have sex in the gametes; sex in the organs that produce 

 the gametes; and sex in the individual that bears- the 

 organs. Beginning with the differentiation of eggs and 

 sperms, differentiation of sex has worked back into the 

 parents which produce them. This is the first time that 

 we have found organisms permanently and wholly male 

 (father.) and female (mother) in a strict sense. In some 

 animals in which sex is distinct the differences between 

 males and females cannot be detected externally, though 

 there are internal differences. 



5. Further Differentiations of Parents. This difference 

 in the sex organs is the most fundamental difference in 

 the parent. All other differences are secondary to these 

 and grow out of them. The task of forming and caring 

 for eggs is so different from the task of forming and caring 



for sperms that the parents, at first differing only in the 

 internal organs that produce gametes, come to differ in 

 many external particulars. This is known as sex- 

 dimorphism. This is the state we are most familiar with 

 in the higher animals and in man. The males and fe- 

 males of most higher animals are more or less 

 conspicuously different from one another. It very often 

 happens that the males of a species of birds, we will say, 

 differ more in general appearance from the familes of that 

 species than they differ from males of an entirely different 

 species. Put in another way, if we were to find the male 

 and female of the rose-breasted grosbeak apart in nature 

 without any chance to find out the facts about them 

 except by external appearance, we should undoubtedly 

 think they belonged to different species. These external 

 differences between males and females of a species are 

 found in birds, in many mammals including man, in some 

 fishes and amphibians, and in many insects. 



6. Nature of External Difference betvneen Male and 

 Female Parents. It is not possible here to call your 

 attention to all the ways in which the bodies of male and 

 female parents differ. The differences are greater in the 

 higher and more active animals. In general the males 

 are more highly colored, stronger, fiercer, and more 

 active. They often have special organs of combat, and 

 instincts to use these. The female is usually more retiring 

 and less endowed with instinct to seek out her mate or to 

 fight other members of the species. Her structures and 

 instincts relate more to care of the young. You can find 

 many illustrations of these statements, as well as some 

 exceptions to them, by field observation of birds; 

 mammals, frogs, insects, and spiders. 



7. The Causes of the Differences. We are reasonably 

 certain that the development of the sex organs and of the 

 cells within these is the chief cause of the differences we 

 see between male and female animals. For example, in 

 the very early development of an individual it is usually 

 impossible to tell which sex an animal is going to be. It 

 is only as the testes and the ovaries develop that the 

 external signs of sex are shown. If we take a male 

 chicken in early life and remove its testes, it will fail to 

 develop spurs and some other extern^ signs of its 

 maleness. Much the same thing is true if the ovaries of 

 a young female chicken are removed. It is much more 

 difficult to see any difference between a male and a 

 female thus deprived of the internal sex organs than 

 between the normal, natural sexes. This shows that it is 

 the sex cells that determine the nature of the parent body 

 rather than that the nature of the parent body determines 

 the sex cells. 



8. The Advantage of these Differences. We know 

 that the developing testes and sperms put into the blood 

 materials that stimulate the growth of the male characters 

 even in such remote parts as the vocal organs, muscles, 

 and so forth. It is the presence of these substances that 

 stimulates the growth of muscles and nervous system. 

 If these substances are absent because of removal, or 

 because of abuse of the developing sex organs, the 

 physical and mental qualities do not develop normally. 



You may wonder what value these differences between 

 males and females have. Or you may take for granted 

 that the sexes should be different and ask no questions 

 about it. Why should the males differ in so many ways 

 from the females? Is there any advantage to the species 

 in having them different? 



We have seen that sperms and eggs stimulate the 

 individuals producing them very differently. There is, 

 however, another side to the matter. The task of the 

 male, the work done by him, and the service rendered 

 the race by the sperm cell and the male parent, are so 



