286 ANIMAL BIOLOGY. [Part II. 



The red fluid contains minute corpuscles, which would seem 

 to be free nuclei. The fluid has not improbably a respiratory 

 function. 



Eespiration. There are no specially differentiated respiratory 

 organs, respiration being apparently effected by the surface 

 of the body. 



The Nervous System. The "brain" or supra-oesophageal 

 mass is divided into two pear-shaped masses, the broad ends of 

 which unite in the middle line. A pair of nerves run forwards 

 from it along the buccal mass to the prostomium. Commissures 

 pass round the gullet to the sub-cesophageal ganglia, which lies in 

 the third segment. Posterior to this there runs a nerve-chain 

 of two conjoined strands, with ganglionic swellings, one for each 

 segment. The swellings are not well marked, and nerve-cells are 

 not restricted to them, but occur throughout the cord. Its 

 sheath is muscular. A pair of nerves is given out on each side 

 from each ganglion, and a single interganglionic nerve on each 

 side in relation to the septa. Around the nerve-chain the septa 

 are incomplete, allowing of communication between the segments. 



The Senses. There are no eyes, but the worm is sensitive to 

 light which falls upon its anterior segments. When suddenly 

 illuminated it dashes like a rabbit into its burrow. It is also 

 somewhat sensitive to radiant heat. There is no organ of hear- 

 ing at present known, but the worm is very sensitive to vibra- 

 tions. It is exceedingly sensitive in the matter of touch, being 

 affected by a very light puff of breath. It does not seem highly 

 sensitive to unnatural odours, but finds out the presence of 

 favourite foods if buried. No organs of taste have been dis- 

 covered, but the worm can apparently distinguish red from 

 green cabbage, and exhibits a decided preference for certain 

 foods, such as carrot, cherry, celery, onion, and horse-radish. 



The Organs of Generation. The earthworm is hermaphro- 

 dite, each individual having both male organs and female organs. 



The Female Organs. Minute ovaries (Fig. 84, B., ovy.\ about 

 $ of an inch in length are attached to the posterior face of the 



