119 



Explain the Structure of Lumbricus as seen in a Transverse 

 Section of the Body, through the Intestinal Region. 



The body- wall consists of a thin cuticle secreted by the 

 underlying ectoderm or epidermis. . Beneath this are two 

 layers of muscles, circular and longitudinal. On each side 

 of the body- wall there are two pairs of chaeta-sacs, pockets 

 of the epidermis in which are the four pairs of chaetae or 

 bristles. 



The space between the muscles and the intestine is the 

 coelome or body - cavity. The " yellow-cells " form an 

 outer coat around the intestine and occupy its deep dorsal 

 fold (the typhlosole). In the " yellow-cells," and above 

 the typhlosole, is the dorsal blood-vessel. Below the in- 

 testine is the ventral nerve cord ; and between it and the 

 intestine is the ventral blood-vessel. Just beneath the 

 nerve cord is the sub-neural vessel. 



I Dorsal blood vessel 



Cuticle . 



- " Yellow-cells" 



\ ] 



Circular muscles 



Typhlosole^ 



Intestin 



Chaeta 



Ventral blood vessel Ventral nerve cord 



Sub-neural vessel 



FIG. 25. Transverse Section of Earthworm (Lumbricus). 



