Chap. 28 



ANNELIDS PIONEERS IN SEGMENTATION 



557 



Mucous tube 

 and 

 cocoon 



Fig. 28.4. Mating earthworms (anterior parts of bodies shown). Every earth- 

 worm has a fully developed male and female reproductive system. During mating 

 each animal transfers sperm cells into the seminal receptacles of the other. The 

 worms become bound together by mucous belts each secreted by a glandular 

 swollen band, the clitellum, conspicuous in all mature worms. After mating, the 

 mucous belts slip off over the heads of the worms, each one gathering up eggs and 

 the transferred sperm cells. Each belt hardens and becomes the cocoon in which 

 fertilization occurs and the embryos develop. The species figured Allolohophora 

 foetida (or Eisenia) is smaller than the familiar Lumhricus terrestris and also very 

 common especially in compost heaps. (Courtesy, Foot: "The Cocoons and Eggs of 

 Allolohophora foetida," Jour, of Morph., 14:38, 1898.) 



through a pore in the cuticle and its other end is in touch with the process 

 of a nerve cell (Fig. 28.5). Light receptor cells are located on the front and 

 rear segments. 



The Inner Tube — Food and Digestion. The body consists of two tubes, an 

 outer one, the body wall, and an inner digestive tube. The space between is the 

 body cavity or coelom, divided into a succession of compartments by par- 



sensorc/ f/ben 



6asa/ membr. 

 ^.sensory ce// 



sensort/ fiber 



nuc/eus 



Fig. 28.5. Gland cells and sense organs in the earthworm's skin. Left, section 

 of the cuticle and skin. The large glands produce the cuticle, the substance that 

 creates the iridescent trails left on sidewalks. Sensory cells receive stimuli and 

 transmit nerve impulses to adjustor nerve cells in the ventral cord. Right, light- 

 sensitive cell, containing a lens-like body (/) and surrounded by retina-like cyto- 

 plasm (r). (Left, courtesy, Curtis and Guthrie: General Zoology, ed. 4. New 

 York, John Wiley and Sons, 1947. Right, courtesy, Hess, Jour. Morph. & Physiol., 

 41:68-93, 1925.) 



