EXPLANATION OF THE PLATE. 



Fig. 1. General view of the viscera of Antiopa cristata, the dorsal skin having been removed: 

 a, buccal organ; b, oesophagus; c, stomach; d, intestine; e, anal nipple ; f,f,f,f, 

 anterior hepatic trunk-tubes; g,g,g, branches from the median hepatic trunk -tube ; 

 h, h, net-work of tubes in connexion with the ramuscules of the hepatic system ; i, a 

 dense glandular mass surrounding the termination of the intestine, apparently in 

 connexion with the hepatic system ; j, ventricle of the heart ; k, auricle ; the oval 

 shadowing marks the extent of the pericardium ; I, small vesicle or portal heart, 

 opening through the floor of the pericardium ; in, portions of the male generative 

 organ ; n, mucus-gland in connexion with the female channel ; o, anterior lobe of ovary; 

 p, posterior lobe of the same ; q, supra-cesophageal ganglia, with various nerves passing 

 from them. 



2. Digestive apparatus of Antiopa cristata, with the hepatic glands of the papillae and the 



net-work of hepatic tubes removed : a, buccal organ ; b, oesophagus ; c, stomach ; 

 d, glandular portion of the same ; e, intestine ; /, anal nipple ; g, g, anterior branches 

 of the anterior hepatic trunk-tube ; h, h, posterior branches of the same ; i, median 

 hepatic trunk-tube giving branches to the papillae of either side on the posterior portion 

 of the body ; j, j, ramuscules leading to the glands of the papillae. 



3. Under or front view of the jaws of Antiopa cristata : a, anterior plate with denticulated 



cutting edge ; b, plain inner cutting edge. 



4. A single jaw of the same, viewed with the cutting edges in front : a, denticulated cutting 



edge ; b, plain inner cutting edge ; c, point of articulation. 



5. Tongue of A. cristata : a, exposed portion exhibiting rows of spines ; b, tubular portion 



of the same. 



6. Central portion of two rows of lingual spines : a, central spine ; b, lateral spines. 



7. A single lateral spine a little more enlarged. 



8. Hepatic gland, removed from papilla ; a, terminal folliculated portion ; b, stem or duct. 



9. Generative organs spread out, the ovary having been removed : a, channel of the penis 



leading to external orifice ; b, retracted penis ; c, testis ; d, constricted portion of the 

 oviduct, as it leaves the ovary ; e, dilated portion of the same ; /, the point where it com- 

 municates with the testis ; g, second dilatation of the oviduct ; h, semi-pellucid portion 

 of the mucus-gland in connexion with the female channel; i, opaque portion of the 

 same; j, female channel leading to external orifice; Ic, spermatheca; /, duct of the 

 same ; m, branch of the duct leading into the mucus-gland near to the female channel ; 

 n, external channel or vagina leading to the spermatheca. 

 10. Cerebral or cephalic ganglia : a, a, cerebroid ganglia ; b, b, branchial ganglia ; c, c, pedial 

 ganglia ; d, d, olfactory ganglia ; e, inner portion of the olfactory nerve, supplying the 

 crest at the base of the tentacles; f,f,f, nerves from the cerebroid ganglia, supplying 

 the lips and channel of the mouth ; g, optic nerve and eye ; li ', nerve to side of body; 

 h, h, pedial nerves ; i, branchial nerve, supplying the sides of the back at the base of 

 the papillae; j, genital nerve, given off from a delicate nervous collar; k, great 

 oesophageal collar; I, buccal ganglia; in, gastro-oesophageal ganglia, each giving off 

 three nerves, which pass to the oesophagus. 



