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 

 coelomic 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 

 coelomic 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 



