32 SEX 



and many of the lower animals feed so easily 

 that economy is not of any account. A single 

 Hydroid polyp developed from a fertilised 

 ovum soon builds up asexually a great colony 

 of thousands of individuals. It must also be 

 remembered that the economy of sexual as 

 against asexual reproduction is in many cases 

 only apparent the wastage of germ-cells 

 being frequently enormous, (b) A second 

 suggestion is that asexual reproduction is 

 incompatible with the complex organisation 

 of a higher animal. We cannot think of a 

 bird multiplying by fission or of an elephant 

 giving off a bud ! They are too highly differ- 

 entiated. No piece of a higher animal could 

 serve as a representative sample of the whole, 

 as an excised piece of polyp does. The 

 possibility of keeping pieces of tissue alive 

 after excision from the body is very much 

 greater than was formerly supposed, but a 

 separated piece of a higher animal is not 

 in natural conditions viable. Now there is 

 doubtless good sense in this suggestion, but 

 it cannot be the complete answer. This must 

 be granted when it is noted that some very 

 complex organisms give off buds, witness 

 the bulbils of the tiger-lily, a highly evolved 

 flowering plant, or the remarkable buds of the 

 beautiful tree-swimming Tunicates known as 

 Salps. The Salp is a very intricate animal, 

 with a much specialised body, and yet it 

 alternates reproduction by germ-cells with 

 reproduction by budding. This is effected 

 by means of a reproductive "stolon" a 

 shoot-like outgrowth containing prolongations 

 from most of the important organs in the 



