134 THE PHYSIOLOGY OF EARTHWORMS 



manufacture of hormone and the gradual refilling of the cells with 

 droplets. When the cells are evacuated the droplets are found 

 distributed along the axons and nerve fibres. When earthworms are 

 exposed to Hght, something which does not happen very often in 

 the field, they show a progressive deepening in colour, and Aros and 

 Vigh (1959) suggest that the neurosecretion is associated with a 

 chromatophorotrophic response. However, no chromatophores or 

 pigment containing cells that are able to expand and contract have 

 as yet been described in earthworms. It is known, moreover, that 

 the pigments of the integument contain protoporphyrin and its 

 methyl esters. Porphyrins are photodynamic and react strongly to 

 light, and in mammals can lead to severe necrotic conditions of the 

 skin. It is thought (Merker and Braunig, 1926) that ultra-violet 

 light is lethal to E. foetida and the animals disintegrate after 

 exposure to this type of Hght ; sunlight is also lethal to earthworms, 

 probably by virtue of the ultra-violet component. More recent 

 experiments (Satchell, personal communication), however, indicate 

 that ultra-violet light is not a lethal factor. It is possible that 

 the darkening of earthworms in Hght is due to photosensitization of 

 protoporphyrin rather than some neuroendocrine response. 



One of the most interesting phenomena encountered in annelids 

 in general, and of which the oligochaetes are a good example, is the 

 ability to be able to replace large portions of the body that are lost 

 by accident or design. Both anterior and posterior regions can be 

 regenerated, the portion being replaced depending upon the 

 position at which transection occurs. If the whole oral complex of 

 ganglia is removed it is only a matter of time before they again 

 appear. But if the ventral nerve cord is removed from the segments 

 immediately adjoining the cut, regeneration takes place only from 

 the cut surface of the nerve cord and not from that of the cut 

 segments (Carter, 1940). Bailey (1930) also found that if the ends 

 of the nerve cord are reflected away from the normal direction of 

 growth then regeneration does not start and the cut surface 

 simply rounds up. Similarly it is possible to induce the formation 

 of a new bud at the site where the nervous system is reflected 

 growing laterally from the body. It is evident, therefore, that the 

 nervous system plays a vital role in the growth of new tissue. 



There is evidence from the amphibia that regenerative ability is a 

 function of the nerves themselves influencing the surrounding 



