Photo: J. J. Ward, F.E.S. 

 GREEN HYDRA 



A little freshwater polyp, about 

 half an inch long, with a crown of 

 tentacles round the mouth. It is 

 Seen giving off a bud, a clear illus- 

 tration of asexual reproduction. 

 When a tentacle touches some 

 small organism the latter is para- 

 lysed and drawn into the moutn. 



'to: J. J. Ward.J'.E.S. 



EARTHWORM 



;arthworms began the profitable habit of moving with 

 end of the body always in front, and from worms to 

 n the great majority of animals have bilateral sym- 



DIAGRAM ILLUSTRATING THE BEGINNING OF INDIVIDUAL LIFE 



1. An immature sperm-cell, with 4 chromosomes (nuclear bodies) repre- 

 sented as rods. 



2. A mature sperm-cell, with 2 chromosomes. 



3. An immature egg-cell, with 4 chromosomes represented as curved 

 bodies 



4. A mature egg-cell, with 2 chromosomes. 



5. The spermatozoon fertilises the ovum, introducing 2 chromosomes. 



6. The fertilised ovum, with 4 chromosomes, 2 of paternal origin and 2 

 of maternal origin. 



7. The chromosomes lie at the equator, an4 each is split longitudinally. 

 The centrosome introduced by the spermatozoon has divided into two 

 centrosomes, one at each pole of the nucleus. These play an important 

 part in the division or segmentation of the egg. 



8. The fertilised egg has divided into two cells. Each cell has 2 paternal 

 and 2 maternal chromosomes. 



G.LASS MODEL OF A SEA-ANEMONE 

 A long tubular sea-anemone, with a fine 

 crown of tentacles around the mouth. The sug- 

 gestion of a flower is very obvious. By means 

 of stinging lassoes on the tentacles minute 

 animals on which it feeds are paralysed and 

 captured for food. 



