876 



LIFE : OUTLINES OF GENERAL BIOLOGY 



evolutionary interpretation. A seed-plant's spores— of two kinds, as 

 in Selaginellas and the like — are the pollen- grains and the embryo- 

 sacs; and the male and female gametophytes are represented by a 

 few nuclear divisions in each, leading to male and female units. It 

 is almost incredible, but it is certain that the sporophyte with its 

 spore-bearing stamens and carpels has practically swallowed the 

 whole of the gametophyte phases; and the seed is a detached 

 megasporangium (or ovule) with an embryo sporophyte enclosed, 

 and with adaptations for nourishment and protection and long 

 lying low. Nature surpassed herself in ingenuity in fashioning the 

 seed. 



Fig. 150, 



Parts of a Flower. A, a cross section through an anther; SP, mother pollen- 

 cells; PG, pollen grains, ia, a pollen grain with two nuclei, and a firm 

 wall (W). 2, diagram of a flower. S, sepal; P, petal; ST A, stamen; PG, 

 pollen grains on the stigma (STI). 3, TN, tube-nucleus; PT, pollen-tube; 

 GN, generative nucleus; S, suspensor cell; OV, ovum or egg-cell; FN, 

 funiculus of the ovule; ES, embryo-sac; AC, antipodal cells. 



ORIGIN OF INSECTS.— In many ways insects have been the 

 most successful of animals. On a very moderate estimate there are 

 a quarter of a million different kinds named and known; and the 

 entomologist is still far from an end of his task. In fact, as was said 

 at the famous breakfast-table long ago, it is hardly possible to be 

 an entomologist, the height of reasonable ambition being to become 

 a Coleopterist, or a Dipterologist, or a Hymenopterist, or even a 

 Myrmecologist. Not only are insects successful in the number of 

 their species, they have sinister powers of multiplying, and they 

 form a cloud in the sky which would soon blot out the sun if it were 

 not for the birds and the bad weather. Insects are found everywhere 

 — even out to sea; they eat almost anything — even theological 

 treatises; they make flowers possible, and they are reincarnated in 

 birds ; their behaviour is an inexhaustible well of surprises, and some 

 of them have social organisations that make us shudder. But all this 

 is shirking the question : Where did insects come from ? 



Remembering King Louis' motto. Divide et impera (split up 

 your difficulties and you will get the better of them) , we divide our 

 problem into sub-problems. This is the only chance of reaching 

 clearness. Our first question is as to the most primitive winged 



