222 SOME PRIMITIVE BELIEFS 



sprout, ro.ot itself, and grow into a completely formed and 

 healthy individual. Animals, too, such as polyps or 

 zoophytes, and many beautiful and elaborate worms, 

 multiply by " fission," dividing into two or more parts, 

 each of which becomes a complete animal. This process 

 is not seen in any fish, amphibian, reptile, bird, or mammal, 

 nor in molluscs, nor in insects, crustaceans, myriapods, and 

 arachnids (spiders and scorpions). It is almost wholly 

 confined to lower animals (worms and polyps) and to 

 plants, and hence is often called " vegetative reproduction." 

 The most remarkable case of its appearance among higher 

 forms is that of the marine ascidians, or tunicates* close 

 allies of the true vertebrates where reproduction by 

 budding and the formation of wonderfully elaborate star- 

 like forms produced by budding and the cohesion of the 

 budded individuals as one composite individual are well- 

 known. Their beautiful shapes and colours have been 

 reproduced in hundreds of exquisite pictures by our great 

 artist-naturalists. We thus have to recognise that there 

 are two distinct kinds of reproduction in living things. 

 One is " asexual," by means of division or separation of 

 large or special masses of their substance, made up of 

 ordinary tissue cells. Co-existing with this, often in the 

 same individuals, is the other method, the " sexual," by 

 means of detached egg-cells and sperm-cells which are 

 thrown off from the parents, and do not (except in rare 

 instances) proceed to develop unless the egg-cell is " fer- 

 tilised " by the fusion with it of a sperm-cell. 



The whole subject of the reproduction of animals and 

 plants was, until the introduction of the microscope, 

 involved in obscurity and mystery. TJie Greeks and 

 Romans had necessarily very imperfect and erroneous 

 notions on the subject, and it was not until 300 

 years ago that William Harvey, the discoverer of the 



* See p. 276 for some account of the Tunicates or Ascidians. 



