42 REPRODUCTION 



has. It has a simple leaf which runs on into a very- 

 tapering, drooping point at its free end. Where this 

 touches the moist ground the tip takes root and a new 

 fern starts. This serves the same purpose as was 

 described for runners. 



6. Division in Many-Celled Organisms. In an earlier 

 chapter we saw how simple plants, such as bacteria, and 

 simple animals, as protozoa, divide into two. It is more 

 difficult to see how a complex animal with special organs, 

 such as mouth, digestive tract, heart, brain, kidneys, and 

 so forth, could possibly divide. Yet this very thing 

 happens quite commonly in animals of the grade of 

 earthworms. It is not true of the earthworm itself, but 

 it is true of other members of the same division of the 

 animal kingdom. 



In worms the division is across the body. Since the 

 mouth, brain, eyes, and other special organs are at the 

 anterior end, these structures must be repeated about half- 

 way back for what is to be the posterior worm. The 

 same is true of the structures that occur at the posterior 

 end. The anterior worm must have a set of these made 

 for him. Of course these new tail structures must lie in 

 front of the new head structures of the rear worm. All 

 these organs usually develop before the two worms 

 separate. We sometimes see four or more such worms in 

 a row, not yet separated, all developed from one worm 

 and soon to break apart. 



In some other types of organisms, as in some of the 

 hydroids, the division is said to be lengthwise. In this 

 case the mouth would be split in two, as would all other 

 such organs. In this way each daughter animal gets one- 

 half of each of the original general organs. 



7. Regeneration of Lost Parts. If a boy cuts a small 

 piece out of his finger, we fully expect the wound to heal. 

 A scar may be formed, but the space is largely filled up 

 and the skin grows over all. This happens so regularly 



