THE ANIMAL ORGANISM 



O.M 



and male, but in some animals both kinds are formed by one 

 individual, which is then known as a hermaphrodite. If sperms 

 are formed before ova, a hermaphrodite is said to be protandrous ; 

 if the ova are formed first, it is protogynous. In some aquatic 

 animals the gametes are set free, and syngamy takes place out- 

 side the body of the parent. In others, however, and in all land 

 animals, the ova are kept within the body of the mother, and the 

 male gametes are transferred in the seminal fluid by the male 

 to the body of the female and there fertilise the ova. This trans- 

 ference is known as coition or copulation. Reproduction in which 



syngamy is necessary before the 

 reproductive bodies can develop 

 is known as sexual reproduction ; 

 that in which the reproductive 

 bodies are not gametes is asexual. 

 In some animals there is a 

 kind of reproduction (partheno- 

 genesis) in which a female germ 

 cell (ovum) develops without 

 syngamy. This kind is best re- 

 garded as an aberrant form of 

 sexual reproduction. 



The terminology of these pro- 

 cesses is in some confusion. 

 Syngamy is the fusion of two 

 cells (p. 498), nucleus with 

 nucleus and cytoplasm with cyto- 

 plasm, though one of the two 

 may have little cytoplasm and possibly sometimes has none. The 

 union of nuclei — which is by far more important than that of 

 the cytoplasms — is karyogamy ; the union of cytoplasm is plas- 

 mogamy. The term conjugation has been used as a synonym 

 for syngamy but is best restricted to the peculiar procedure by 

 which syngamy is accomplished in the Ciliata (Chap. 5). 



Fig. 4. — The"^ovum of a bat, after 

 the entry of the spermatozoon. — 

 From F. H. A. Marshall, after 

 van der Stricht. 



o.n., nucleus of the ovum ; p.b., ' polar 

 bodies ' (see p. 620) ; spn., spermatozoon. 



ACTIVITY 



Most familiar animals, and some plants, may be said to be 

 active in a way in which a stone is not, although machines have 

 a certain type of activity which simulates that of living things. 

 The activity may be the result of the receipt of a stimulus, that 



