482 TARDIGRADA CHAP, 
The nervous system consists of a brain cr supra-oesophageal 
ganglion, whose structure was first elucidated by Plate, and a 
ventral chain of four ganglia. Anteriorly the brain is rounded, 
PE fee and gives off a nerve to the skin ; 
7 === posteriorly each half divides into 
' two lobes, an inner and an outer. 
The latter bears the eye-spot when 
this is present. Just below this 
eye a slender nerve passes straight 
to the first ventral ganglion. The 
brain is continued round the oral 
cavity as a thick nerve-ring, the 
ventral part of which forms the 
Fic. 253.—Brain of Macrobiotus hufel- sub-oesophageal ganglion, united 
andi, C. Sch., x about 850. (From by two longitudinal commissures 
Plate.) Seen from the side. ap, Lobe Z 
of brain bearing the eye; ce, supra- tO the first ventral ganglion. 
oesophageal ganglion; d, tooth; Ga, Thus the brain has two channels 
first ventral ganglion ; ga’, sub-oeso- : f : 
phageal ganglion ; &, thickening of the Of Communication between it and 
epidermis round the mouth ; oc, eye- the ventral nerve-cord on each 
spot ; 0e, oesophagus ; op, nerve run- 
ning from the ocular lobe of the brain side, one by means of the slender 
ee ie ventral ganglion; ph, nerve above mentioned, and one 
through the — sub - oesophageal 
ganglion. The ventral chain is composed of four ganglia con- 
nected together by widely divaricated commissures. Each 
ganglion gives off three pairs of nerves, two to the ventral mus- 
culature, and one to the dorsal. The terminations of these 
nerves in the muscles are very clearly seen in these transparent 
little creatures, though there is still much dispute as to their 
exact nature. 
The older writers considered the Tardigrada as hermaphrodites, 
but Plate and others have conclusively shown that they are 
bisexual, at any rate in the genus JJacrobiotus. The males are, 
however, much rarer than the females. The reproductive organs 
of both sexes are alike. Both ovary and testis are unpaired 
structures opening into the intestine, and each is provided with 
a dorsal accessory gland placed near its orifice. In the ovary 
many of the eggs are not destined to be fertilised, but serve as 
nourishment for the more successful ova which survive. 
No special circulatory or respiratory organs exist, and, as in 
many other simple organisms, there is no connective tissue. 
