62 



THE EARTH-WORM 



with "yellow-cells." The wall of the intestine is composed of a 

 muscular layer, and is lined with ciUated epithelium. ..... 



(i) The dorsal blood-vessel, lying in the " yellow-cells » above the intestme. 



( /) The ventral or sub-intestinal blood-vessel, lying beneath the mtestme. 



(fc) The ventral nerve cord, lying beneath the ventral blood-vessel. Just 

 beneath the nerve cord is the sub-neural vessel. 



(I) Portions of the septa, and portions of nephridia. 



Dorsal Vessel 

 Typhlosole 



Cuticle 

 Epidermis 



Circular Muscles 



Longitudinal Muscles 



Setas 

 Nephridium 



Yellow-cells " 



External Aperture of 

 Nephridiuin(nephridiopore) 



Nephrostome 



ventral Nerve Cor^^^^^^^^^^' 'Coelome"" Set» 

 ^^^^ fS^S^^ ^^ Ventral Vessel 

 Sub-neural Vessel 



Fio. 21. — Transverse Section (diagrammatic) through the middle of the body of the 

 Earth-worm (Lumbricus). A nephridium is shown (entire) on the left side of the 

 figure, and setae on the right side. After Marshall and Hurst. With permission 

 from Parker and Haswell's Text-book of Zoology. 



Carefully remove one of the ovaries, along with the portion of the septum to 

 which it is attached and with the attached nephridium. Mount on a slide in 

 salt solution, and examine with a low power. Notice the ripe ova in the thin 

 distal end of the pear-shaped ovary. The nephridium is tubular and consists 

 of a very small ciliated funnel, a looped main portion which is glandular and 

 solid (the duct passes through the cells), and a much wider and non-glandular 

 bladder which opens to the exterior. The bladder has muscular walls, and 

 within it may be seen parasitic Nematode worms. The ciliated funnel opens 

 into the coelome or body-cavity, and this internal opening is the nephrostome. 

 Notice the blood capillaries on the walls of the nephridium. 



The contents of the seminal vesicles and the spermathecae should be 

 examined under high power. The first contain developing spermatozoa, and 

 the second have ripe spermatozoa received from another worm. 



Note. — The South African Earth-worm (Chilota) is very suitable for dis- 

 section, especially with reference to the reproductive system, and should 

 therefore be studied by senior students if possible. 



