GROWTH AND SEXUAL GENESIS. 453 



of the relation between small size and active gamogenesis 

 among low types of the Metazoa is supplied by the Rotifera. 

 Microscopic as these are, they have a great rate of sexual 

 increase. According to Ehrenberg, Hydatina senta " is 

 capable of a four-fold propagation every twenty-four or 

 thirty hours, bringing forth in this time four ova, which grow 

 from the embryo to maturity, and exclude their fertile ova 

 in the same period. The same individual, producing in ten 

 days forty eggs, developed with the rapidity above cited, this 

 rate, raised to the tenth power, gives one million of indi- 

 viduals from one parent, on the eleventh day four millions, 

 and on the twelfth day sixteen millions, and so on." 

 Ehrenberg, however, characterized by Huxley as " the 

 greatest looker and the worst observer," is not a safe autho- 

 rity, and it is better to state the estimate of Ludwig Plate, 

 who says that Hydatina lays fifty eggs in two to three weeks 

 a number which, multiplying in the manner described, 

 will yield in the time named a much smaller total though still 

 an enormous total. 



The Annul osa, including among them the inferior types, 

 have habits and conditions of life so various that only the 

 broadest contrasts can be instanced in support of the pro- 

 position before us. The differences of organization and 

 activity greatly complicate the inverse variation of fertility 

 and bulk. Bearing in mind, however, that the rate of multi- 

 plication depends much less on the number of each brood 

 than on the quickness with which maturity is reached and a 

 new generation commenced, it will be obvious that though 

 Annelids, relatively enormous in size, produce great numbers 

 of ova, yet as they do this at comparatively long inter- 

 vals, their rates of increase fall immensely below that just 

 instanced in the Kotifers. And when at the other extreme 

 we come to the large articulate animals, such as the Crab 

 and the Lobster, the further diminution of fertility is seen in 

 the still longer delay which occurs before each new generation 

 begins to reproduce. 



