CHAPTER LXIX 



RELATIONS BETWEEN ANIMAL ORGANISMS 



From time to time, in reviewing the different phyla, relations between 

 organisms have become apparent, and some of these have been indicated 

 by name. It is, however, desirable to pass in review these relationships 

 in such a manner that the logical connection between them will appear. 



553. Solitary Life. — Solitary life is a possible mode of living only 

 to those organisms which are able to play their part in reproduction with- 

 out relation to any other individual. Examples would be the simpler 

 protozoans, like the ameba, which reproduce by fission; and some meta- 

 zoans, which reproduce by budding. It may also occur, as far as the indi- 

 vidual is concerned, in the case of some sexual organisms, like clams and 

 mussels, the males of which simply pass their sperm cells out into the 

 water, chance alone determining their entrance into the female and the 

 fertilization of the egg cells. Since, however, most animals, even though 

 they may live alone at other times, come together at the time of breeding, 

 a strictly solitary existence is a rare phenomenon. 



554. Associations of Animals of the Same Species. — Associations of 

 this type have their logical beginnings in the relation of animals as mates 

 and also include families, colonies, and societies. 



555. Mating. — Mating refers to the association of two individuals 

 for purposes of reproduction, one taking the part of the male and the 

 other that of the female. Such an association may be an exceedingly 

 temporary one, ending as soon as the eggs have been fertilized, or, 

 on the other hand, it may be a relationship which lasts throughout the 

 lifetimes of the individuals concerned. As a general principle animals 

 low in the scale of animal life exhibit a mating which is quite temporary, 

 but in ascending the scale the relationship is found to be gradually pro- 

 longed. Especially is this true of animals in which the care of the 

 parents is necessary for the successful rearing of the young. The mating 

 of one male with several females is termed 'polygamy; and of one female 

 with several males, polyandry. 



556. Families. — If the offspring remain together and are accompanied 

 by the parents, the relation is that of a family. This may persist only 

 until the young are able to care for themselves, which is true of birds and 

 mammals generally, or, on the other hand, it may last longer and lead to 

 the next type of association. 



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