132 ANIMAL BEHAVIOUR 



In many Protists the body is a cell which simply absorbs materials 

 over all or part of its surface. But, in general, animals nourish 

 themselves and in the course of their nutrition exhibit char- 

 acteristic forms of behaviour. Thus : 



i. Hunting for food organisms as in the exceedingly simple 

 way of an Amoeba (using pseudopodia), or by the more elaborate 

 methods of a cuttle-fish (the use of the tentacular apparatus, the 

 suckers and the beak) ; or by the craft of a cat, or fox, or man. 



a. Trapping and snaring, with fabrication of the trap or snare 

 (as in the case of the spider's web). 



Hi. Browsing as in the cases of terrestrial herbivores, many 

 molluscs and some fishes. 



iv. Filtration as in the cases of sponges, sessile molluscs, 

 herrings, whalebone whales, etc. And so on, these are only 

 examples of typical ways in which the animal obtains, via its bodily 

 motions, the environmental materials which it assimilates. 



47&. Manifestations of the Growth-urge. Growth of the 

 body, or of a part of the body, is a functional metabolic activity 

 not strictly to be associated with ways of behaviour in the technical 

 sense in which we use the term. The essential acts of reproduc- 

 tion are the maturations, divisions and fertilizations of germ-cells. 

 Maturations and mitoses are functional activities and, in them- 

 selves, the conjugation of two germ-cells, or even gametes, are also 

 functional in the same sense. In the cases of very many animals 

 reproduction is accompanied by little in the nature of behaviour. 

 Thus a Teleostean fish, as a rule, experiences a ripening of its 

 gonads and when the eggs or spermatozoa have become mature 

 they are simply extruded into the sea where conjugation of the 

 gametes occurs at random. In a sessile Barnacle (which is herma- 

 phrodite) the ova and spermatozoa mature in the body, self- 

 fertilization may occur, embryos develop, hatch from their 

 envelopes and are extruded into the sea. The general behaviour 

 of the parent is, so far as we can see, unaff"ected by all this. 



But in a vast number of animals the growth-urge in reproduc- 

 tion is attended by the most complex behaviouristic activities. 

 We notice typical examples : (i) Breeding and spawning migrations. 

 Locomotion is involved. Birds make extensive and specially 

 directed flights. Salmon ascend rivers to spawn. Eels descend 

 rivers and seek the mid-ocean to spawn. Cod, plaice, herrings. 



