MANUAL OF ELEMENTARY ZOOLOGY 



two distinct portions of living matter. The bodies which 

 unite are known as gametes and that which results from 

 their fusion as a zygote. In large and complex animals con- 

 jugation takes place only between the 

 reproductive bodies, which are generally 

 unable to develop without it, so that, 

 as we have seen, it becomes a part of 

 the reproductive process. In these cases 

 the reproductive bodies are of a kind 

 known as germs, distinguished from other 

 reproductive bodies by their small size 

 and the simplicity of their structure. 

 The germs of such animals are, as has 

 been said, of two sorts. One is larger 

 and passive, and is known as the egg, 

 ovum, or female gamete. The other is 

 smaller and active, and known as the 

 spermatozoon or male gamete; it moves 

 to the egg and enters it, and is then said 

 to fertilise it. Ova and spermatozoa are 

 usually formed by different adults, known 

 respectively as female and male, but in 

 some cases both kinds are formed by one 

 individual, which is then known as a her- 

 maphrodite. In some aquatic animals the 

 gametes are set free, and conjugation takes 

 place outside the body of the parent. In 

 many cases, however, the ova are kept 

 within the body of the mother, and the 

 male gametes, known collectively as the 

 sperm, are transferred by the male to the 

 Fig. 3. — Human body of the female and there seek and 

 spermatozoa, fertilise the ova. This transference is 

 highly magnified, kn0wn as coition Reproduction in 

 seen in face and m . . . . . r , . 



side view.— After which conjugation is necessary before 

 various authors, the reproductive bodies can develop is 

 known as sexual reproduction. That in 

 which conjugation does not take place is asexual. We 

 shall see (Chap. VII.) that in some of the smallest 

 animals conjugation takes place, not between newly 

 formed germs, but between fully grown adults, and has 



