130 Animal Life and Intelligence, 



individual. In the higher forms of animal life, the organisms 

 are either female (egg-producing) or male (sperm-pro- 

 ducing). But there are many hermaphrodite forms which 

 produce both eggs and sperms, as in the common snail and 

 earthworm. Even in these cases, however, there are 

 generally special arrangements by which it is ensured that 

 the sperm from one individual should fertilize the orum 

 produced by another individual. 



What, we must next inquire, is the relation in the higher 

 forms of life for we may now leave the special considera- 

 tion of hydra of the ovum or sperm to the organism which 

 produces it ? This is but one mode of putting a very old 

 question Does the hen produce the egg, or does the egg 

 produce the hen ? Of course, in a sense, both are true ; 

 for the hen produces an egg which, if duly fertilized, will 

 develop into a new hen. But the question has of late been 

 asked in a new sense ; and many eminent naturalists reply, 

 without hesitation The egg produces the hen, but under 

 no circumstances does the hen produce the egg. What, 

 then, it may be asked, does produce the egg ? To this it 

 is replied The egg was produced by a previous egg. At 

 first sight, this may seem a mere quibble ; for it may be 

 said that, of course, if an egg produces a hen which contains 

 other eggs, these eggs may be said to be produced by the 

 first. But it is really more than a quibble, and we must do 

 our best clearly to grasp what is meant. 



We have seen that, in development, the fertilized egg- 

 cell undergoes division into two cells, each of which again " 

 divides into two, and so on, again and again, until from 

 one there arises a multitude of cells. Nor is this all. The 

 multitude are organized into a whole. The constituent 

 cells have different forms and structures, and perform 

 diverse functions. Some are skeletal, such as bone and 

 connective tissue ; some are protective, such as those which 

 give rise to feathers or scales ; some form nerves or nerve- 

 centres ; some, muscles ; some give rise to glandular tissue; 

 and lastly, some form the essential elements in reproduc- 



