vi REPRODUCTIVE ORGANS 345 



in any of the lower organisms described in the five 

 previous chapters. 



Notice in the second place the vastly greater com- 

 plexity of microscopic structure, the body being divisible 

 into tissues (p. 118), each clearly distinguishable from the 

 rest. We have epithelial tissue with its cuticle, mus- 

 cular tissue, and nervous tissue, as well as blood and 

 ccelomic fluid. One result of this is that, to a far greater 

 extent than in Hydra, we can study the morphology of 

 the earthworm, as we have done that of the frog, 

 under two distinct heads : anatomy and histology 

 (p. 104). 



Asexual reproduction does not take place normally in 

 the earthworm, but it frequently happens by accident 

 that a worm is cut into two or more parts. When 

 this occurs, each end is able to reproduce the missing 

 portion : this process is known as regeneration (compare 

 pp. 268 and 307). 



The earthworm, like Hydra, is monoecious or herm- 

 aphrodite (p. 307) , and besides the essential organs of 

 sexual reproduction ovaries and spermaries which 

 are, as in the frog, developed from certain parts of the 

 ccelomic epithelium (p. 604), it possesses various 

 accessory organs. The whole reproductive apparatus 

 is situated in segments 9-15. 



The ovaries (Figs. 82, ov, and 86, o) are a pair of minute 

 bodies about I mm. in length, attached by a short stalk, 

 one on either side, to the posterior face of the septum 

 separating segments 12 and 13, not far from the 

 nerve-cord. The proximal end of each ovary, nearest 

 the stalk, is composed of a mass of undifferentiated cells 

 of germinal epithelium (compare Figs. 62 and 63) : 

 nearer its middle, certain of these are seen to increase in 

 size so as to be recognisable as young ova : while the 



