768 



LIFE : OUTLINES OF GENERAL BIOLOGY 



to die after spawning, so that the ageing part of its life-curve is 

 almost like a perpendicular. Lord Avebury kept two queen-ants of 

 different species for nine and fifteen years respectively; what a 

 contrast to the life-curve of one of the Mayflies or Ephemerids, 

 which is said to have an adult life of a single hour ! 



This idea of the adjustability of the length of different arcs on 

 the life-curve points on to the interpolation of larval stages. Out of 

 the egg of a cockroach, locust, earwig, or spring-tail, there emerges 

 what is almost a miniature of the adult; and there can be little 

 doubt that this is the primitive kind of life-history among insects. 



Fig. 125. 



Alternation of Generations. After AUman. A, a magnified portion of an 

 asexual hydroid or zoophyte colony; h, an ordinary nutritive polyp or 

 hydranth; m, an almost complete reproductive bud or medusoid; p, 

 external investment or perisarc. B, a liberated sexual swimming bell or 

 medusoid; ma, manubrium or mouth-tube; fic, radial nutritive canal; 

 s, sense-organ; tentacles hanging down. 



But, as everyone knows, all the higher insects have their life-history 

 complicated by the occurrence of larvae, such as caterpillars and 

 grubs; and it seems that these larval phases have been secondarily 

 interpolated in adaptation to seasons and circumstances. The 

 winged adults are more or less specialised for reproduction; the 

 larval stages are specialised for nutrition and growth. In some 

 cases the adult insects do not feed at all; and with one exception 

 (Mayflies) there is no moulting after the winged stage is reached — 

 which is another advantage of the larval parenthesis. 



From indirect or circuitous development, with larval stages and 

 metamorphosis, it is but a step, though a large one, to Alternation 



