vi REPRODUCTIVE ORGANS 345 



structure and division of physiological labour play a far 

 more obvious and important part than in any of the 

 lower organisms described in the five previous chapters. 



Notice in the second place the vastly greater complexity 

 of microscopic structure, the body being divisible into tissues 

 (p. 1 1 8) each clearly distinguishable from the rest. We have 

 epithelial tissue with its cuticle, muscular 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 p. 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 epi- 

 thelium, it possesses various accessory organs. The whole 

 reproductive apparatus is situated in segments 9-15. 



The ovaries (Figs. 82 0v, 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 twelve and thirteen, 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 distal end 



