RESULTS OF ASEXUAL REPRODUCTION 295 



Before leaving this subject an important distinction 

 between budding and fission should be noted. An organ- 

 ism may produce a few or many buds, but it ultimately 

 dies. In fission, on the other hand, the parent vanishes 

 in the creation of two descendants out of the same mate- 

 rial and no death occurs (see Chap. XXII). 



Results of Asexual Reproduction. — The upper 

 limits of sexual activity are reached in the case of the 

 shipworm or teredo and certain species of tapeworms that 

 lay 70,000,000 eggs a year; yet even this number of in- 

 dividuals is far short of what is known to be asexually 

 produced in much less time by many unicellular organ- 

 isms. In Stylonychia, a close relative of Paramcecium, the 

 body divides once in every eight hours. In six days, if 

 favorable conditions could be maintained, the number 

 of offspring would be countless and their combined mass 

 would weigh approximately fourteen pounds. In thirty 

 days the aggregate, it has been estimated, would be a 

 million times greater than the sun. Although such exces- 

 sive numbers are never realized, there is rapid multipli- 

 cation during favorable periods, and some cells are cer- 

 tain to be carried into situations sufficiently favorable 

 to enable them to persist. 



It will be seen that while this mode of reproduction 

 tends to produce almost unlimited numbers, it obviously 

 produces individuals that closely resemble each other. 

 Sexual reproduction, on the contrary, for reasons that will 

 be shown in a subsequent chapter, is much more likely to 

 result in offspring that are unlike and are therefore more 

 favorable subjects for the process of evolution. 



Regeneration. — Regeneration is the ability of an 

 animal or plant to replace lost parts. In certain species 

 among the lower animals this may lead to the production 

 of new individuals, and thus be a form of asexual repro- 

 duction. The sponges, many relatives of hydra, worms 

 of various kinds, the starfishes, and several other animals 

 are without firm protective envelopes and hence are sub- 



