EARTHWORM. 217 
pharynx ; the dorsal and the supra-neural are linked together 
in the region of the gullet by five or six pairs of contractile 
vessels or “hearts.” 
‘ Respiration is effected by the distribution of blood on 
the general surface of the skin. 
Excretory system.—There is a pair of nephridia in each 
segment except the first four. Each opens internally into 
the segment in front of that on which its other end opens 
to the exterior. They remove little particles from the body 
cavity, and get finer waste products from the associated 
blood vessels. Nephridia occur in many animals, in most 
young Vertebrates as well as among Invertebrates, but they 
are never seen more clearly than in the earthworm. When 
a nephridium is carefully removed, along with a part of 
the septum through which it passes, and examined under 
the microscope, the following three parts are seen :— 
(a) An internal ciliated funnel; (4) a trebly coiled ciliated 
tube, at first transparent, then glandular and granular; and 
(c) a muscular duct opening to the exterior. Minute par- 
ticles swept into the ciliated funnel pass down the ciliated 
coils of the tube, and out by the muscular part which opens 
just outside of the ventral bristles. The coiled tube con- 
sists in part at least of a series of intracellular cavities, that 
is to say, it runs through the middle of the cells which 
compose it; the external muscular portion arises from an 
invagination of skin. 
Reproductive system.—Like all Oligochetes, the earth- 
worm is hermaphrodite and the organs complex. The 
complexity is produced by the specialisation of certain of 
the nephridia to form genital ducts and accessory organs 
and by the presence of chambers (seminal vesicles) con- 
nected with the testes, formed by the shutting off of portions 
of the body cavity. 
The organs in the earthworm are difficult to dissect, and 
differ considerably in old and young specimens. 
(a) The Male Organs consist of two pairs of testes, three 
pairs of seminal vesicles, and paired vasa deferentia. 
(1) The testes, flattened lobed bodies, about ,/5 in. in size, 
arise from proliferations of the peritoneal lining of the body 
cavity, and are invested by a delicate membrane derived 
therefrom; they lie near the nerve-cord, attached to the 
