282 General Biology 



mer forming the mouth or stomodeum ( ), the latter 



the anal opening or proctodeum ( ). 



The chlorogogen cells are formed from mesoderm, as are also the 

 blood-vessels, muscles, reproductive organs and seta sacs. The young 

 worm is now ready for an independent life and leaves the cocoon after 

 from two to three weeks. 



The following table will give a summary of the important tissues 

 derived from the various germ-layers : 



ENTODERM ECTODERM MESODERM 



Oesophagus, Outer Epithelium, Muscles, 



Crop, Nervous System, Coelomic Endothelium, 



Gizzard. Stomodeum, Chlorogogen Cells, 



Proctodeum, Calciferous Glands, 



Ends of Nephridia. Blood vessels, 



Septa, 



Nephridia, functional parts, 

 Seta Sacs, 

 Reproductive Organs. 



BEHAVIOR 



As shown by their home-life, worms are apparently fond of having 

 their bodies in contact with solid objects. Moisture causes a positive 

 reaction if such moisture comes in direct contact with the worm's body. 

 This is well illustrated by placing the earthworm, Allobophora foetida 

 (the small manure worm), on a piece of dry filter paper when it will 

 not react, but as soon as moisture is applied it begins to burrow, pro- 

 vided this moisture or liquid is taken from manure. 



Darwin supposed that the earthworm's ability to distinguish edible 

 from inedible food lay in the sense of contact. This would make contact 

 in the earthworm act as a sort of taste organ. Various chemicals which 

 cause a reaction, may be due to this sort of secondary taste-ability. 



While there are no eyes, light causes the animal to react. This is 

 shown by its moving away from lighted areas. The manure worm, how- 

 ever, will respond positively to a very faint light. The preferable colors, 

 when very faint, are red, green and blue in the order given, though it 

 does not follow from this that the earthworm can distinguish colors. 

 Its ability consists, in all probability, of ''feeling" different rays of light 

 as well as different intensities. 



It has also been noted that, if a previous stimulus is much stronger 

 than a succeeding one, the first will naturally continue to react and 

 cause either no reaction to a second or at least lessen such reaction. 

 An example of this is found when the animal is feeding or mating. Light 

 which under normal conditions causes a negative reaction, may have 

 no effect whatever under such circumstances, the instinctive reaction 

 of the primary instinct being stronger than the artificial secondary 

 stimulus. 



