TRITONIA. 



posterior portions or branchial ganglia give off, from the upper surface behind, a pair of large 

 nerves (8) which supply the dorsal skin ; and the right branchial furnishes an additional single 

 nerve (7) to the root of the male intromittent organ. This is the only one we have traced of 

 the visceral nerves though doubtless others exist. The pedial ganglia (c, c) are round, and 

 united by short commissures to the cerebroid and branchial. They give off three pairs of 

 stout nerves (9, 10, 11), which are distributed to the foot. The great sub -oesophageal collar 

 {h) is wide, and is composed of three filaments, two of which belong to the pedial ganglia, — 

 one to the branchial. 



The buccal ganglia (/) are situated as usual on the buccal organ, immediately behind the 

 gullet ; they are rather large, broadly elliptical, and united across the median line by a short 

 commissure, and to the under side of the cerebroids by two long cords (i, i) forming the 

 buccal collar. These ganglia give two pairs of nerves (12, 13) to the buccal organ, and a 

 single one (14) to the tongue ; the latter comes off from the commissure uniting the ganglia. 

 They have also appended to them by much longer cords than usual, a pair of gastr- 

 oesophageal ganglia (g,g) ; these supply, besides the oesophageal nerves (17) (the par vagum), 

 two other pairs, one of which (15) goes to the salivary glands, the other (16) to the root of the 

 oesophagus. 



The senses are in the same condition as in Boris. The eye [j ) is small, and is removed 

 to a considerable distance from the cerebral ganglia. The optic nerve is consequently long ; 

 it is very delicate and arises from a small ganglionic enlargement (e) seated above and behind 

 on the outer margin of the cerebroids. The auditory capsules have not been examined in 

 T. Hombergii, but in T. plebeia, in which the cerebral ganglia are similar, they contain 

 numerous otolithes (fig. 12 e), and are sessile on the under surface of the cerebroid ganglia, a 

 little in advance of the commissures (d), which unite these ganglia to the pedial. Taste 

 probably resides in the lips, touch everywhere, but is speciallised in the tentacular points of 

 the veil. 



The skin is devoid of spicula, and is thick and coriaceous. 



EXPLANATION OF THE PLATE. 



Fig. 1. General view of the viscera of Tritonia Hombergii, the dorsal skin laid open : — a, buccal organ; 

 b, oesophagus ; c, c, salivary glands ; d, anterior portion of the stomach ; e, intestine ; /, liver 

 enveloped in the ovary; g,g, portions of the mucus-gland in connexion with the female 

 organs ; h, retracted penis ; i, portion of the testis ; j, pericardium ; k, ventricle, seen through 

 the transparent wall of the pericardium ; I, auricle ; m, m, lateral venous trunks, or efferent 

 branchial veins, passing from the skin to the^ auricle; n, n, branches of the same laid open, 

 showing orifices communicating with the gills and cellular tissue of the skin ; o, o, o, afferent 

 branchial veins from the liver-mass; p,p, branches of the same exposed, giving twigs to the 

 branchial plumes ; q, portal heart seen through the transparent walls of the pericardium ; r, 

 oesophageal ganglia, giving nerves to the various organs ; s, s, the eyes. 

 2. General view of the viscera, the various organs partially separated : — a, buccal organ ; b, 

 oesophagus ; c, c, salivary glands ; d, stomach ; e, e, intestine cut through ; f, liver enveloped 

 in the ovary; g, root of the aorta, the ventricle removed ; h, anterior branch of the same ; i, 



