If a lizzard loses its tail, it is said that it does in some 

 degree grow again. In crayfishes, if antennae or other 

 appendages be lost, new ones may grow out. This 

 suggests that this power is seen to better advantage in 

 the lower than in the higher animals. It is even more 

 true in animals still lower. In the earthworm it has been 

 shown that the head, brain, mouth and all" necessary 

 anterior organs may be cut away. If this is done, some 

 six or eight segments back of the head all these lost 

 organs will be formed again in front of the cut. Similarly, 

 new posterior organs will be regenerated if posterior 

 segments are removed. 



In hydra, which is one of the very simplest of the many- 

 celled animals, it is said that any length of the body 

 anywhere may be able to regenerate all the lost parts. 



CHAPTER EIGHT. 

 RELATIONS OFBARENTS AND THBIROFFSPRING 



1. Parental Sacrifice. In all these kinds of reproduction 

 you have studied you see that to form the offspring is a 

 drain on the parent. A part of the parent's body goes 

 directly to form each of the young, or some special 

 growth takes place from the parent which • forms the 

 young, and in doing so uses up food materials that might 

 have gone to strengthen the parent instead. This 

 sacrifice is the one unvarying fact in all the varying 

 methods of reproduction. 



2. The Species and the Individual. In such plants and 

 animals as we have been studying, all that an individual 

 can do for the species is to reproduce offspring. This is 

 the very simplest and easiest form in which to introduce 

 individual sacrifice for the race. The species flourishes in 

 proportion as individuals first build themselves up, and 

 then reverse matters and exhaust themselves in putting 

 offspring on the way to success. 



3. The Degrees of the Sacrifice. While all plants and 

 animals seem driven by their nature to make this sacrifice, 

 there seems to be a distinct tendency, as we go up the 

 scale, to make the sacrifice as light as possible and still 

 do the work. At least we find it very much lighter in 

 some organisms than in others. For example, we saw in 

 the bacteria and some other simple forms that the parent 

 was at once completely destroyed in forming the two 

 offspring. In the yeast, on the contrary, the new cells 

 bud off from the old and the parent continues its own 

 life alongside the new offspring. Two offspring cost 

 much less of the body of the yeast parent than in bacteria. 

 In the case of spores, the sacrifice is still less. Only a 

 .small part of the parent enters into them. 



4. The Size and Number of Offspring. In the bacteria 

 the two offspring are each just one-half the size of the 

 parent. The same is true of all other forms that 

 reproduce by simple division, as some worms. This is an 

 expensive method. Only two offspring are formed in 

 these cases and the parent is entirely destroyed. In the 

 case of the yeast, the parent produces much smaller 

 offspring to start with and then allows it to grow up to 

 standard size. This is even more true in the forms that 

 produce spores. Many of these may produce thousands 

 of spores which are only a minute fraction of the size of 

 the parent plant. The parent may be completely used up 

 in this process or may use a part of its energies, leaving 



some of its strength for reproduction some other time. 



5. How the Problem is Solved. It may help the student 

 understand what happens in different organisms to see 

 what possible solutions there are. In reproducing, parents 



1. May be completely destroyed: 



(a) By producing two offspring, each one-half the 

 size of the parent, as in the bacteria and other 

 forms that simply divide. 



(b) By producing several or many minute offspring, 

 as in some cases of reproduction by spores. 



2. May not use up all their substance in reproduction: 



(a) Producing a few young, but much smaller 

 than one-half the parent when first produced. 

 Such are the budded cells in yeast or the 

 young strawberry plants formed by runners. 

 Here the offspring is of new substance made 

 by the parent rather than the old substance 

 of the plant itself. 



(b) Producing a large number of minute young in 

 particular portions of the body. Not all the 

 parent is used up. This is the case in many 

 plants. 



It should be remembered that many organisms which 

 are not actually destroyed outright by the formation of 

 their young are still so exhausted by producing and 

 maturing them that they die, and do not reproduce again. 

 All our annual herbs would fall in this class. 



6. The Problems Related to the Size and Number of 

 the OfTspring. We know that in the long run an animal 

 or plant only needs to bring one of its offspring to 

 complete maturity during its own life in order to leave 

 the species as well represented as before. But there are 

 many disasters between the young and their maturity. 

 Therefore very many more must be produced than will 

 ever come to maturity. This is true of all organisms. If 

 all the offspring that any species can produce were to 

 live and mature and produce indefinitely, that species, 

 in a few years, would become a pest. Many must be 

 produced in order to insure one. 



Now the advantage in having offspring like the bacteria, 

 one-half grown at birth, is very clear. It only takes a 

 little time for it to become adult, and the dangers that it 

 will not do so are less than if it were one-thousandth part 

 of the adult. On the other hand, the parent was completely 

 destroyed and we have only two of the half-grown 

 offspring instead of the one adult. The advantage of a 

 form that produces thousands of small offspring is that 

 there is more chance of one in a thousand surviving than 

 of one in two, and beside they can be scattered over a 

 wider territory and this increases their chance. On the 

 other hand, these small young have much further 

 to go in developing and the chances of disaster 

 are correspondingly increased. It is more expensive to 

 produce large offspring, but they are nearer their goal. 

 With a given outlay many more of the small offspring can 

 be produced, but they are not so sure. Each method has 

 its advantages. 



7. The Tendency to Diminish the Size of OfTspring. As 

 we come up to the plant and animal kingdom, we find that 

 the size of that part of the parent which enters into each 

 of the offspring is decreased. We find further that less 

 and less of the substance of the parent is given up to 

 making offspring, and that more of the parental body is 

 left to live and reproduce again and again through a 

 considerable period. Thus, instead of parents dyino- in 

 producing the offspring, the parents may live along side 

 by side with them for a considerable period. By this 

 means the parent may produce even more offspring than 

 if it gave all its substance to offspring at the outset; and it 

 may distribute them through a better period of time. 



