POLYCERA. 



P. Lessonii is a little dilated just before it terminates. A small oval sac, apparently the 

 same as the pancreatic organ in Boris, opens into the stomach near to the oesophagus in P. 

 ocettata : a similar organ probably exists in the other species, but has escaped observation. 

 The liver (y) is of a brownish yellow colour, of an oval form, with the anterior extremity trun- 

 cated ; its secretion passes into the stomach through three or four openings. 



The reproductive apparatus in P. quadrilineata is much like that of Idalia. The testis is 

 divided into three portions ; that (&') next the intromittent organ {Ji) is moderately thick and 

 tubular : the inner extremity of this portion is swelled a little, and is succeeded by an attenu- 

 ated tube (i") having a duct-like appearance, which leads to one end of a large, irregularly 

 oval, glandular organ (i), presenting the semblance of a laminated structure ; the other ex- 

 tremity of this portion is united by a short tube {%") to the oviduct. The ovary is spread out 

 as usual over the liver, and the oviduct is at first slender, (j) and afterwards much dilated (/) 

 as it reaches the testis. The vaginal tube (/) is rather long and slender ; it opens into the 

 obtuse end of a very large pyriform spermatheca (m). A long, delicate duct (n), passes from 

 the same point to the oviduct, and has attached to it a small oval sac — a second spermatheca 

 (o). The mucus-gland (k) is much convoluted. 



The generative organs, in P. ocettata and P. Lessonii are s'milar to those of P. quadrilineata, 

 differing only in unimportant modifications. In the former, the glandular portion of the testis 

 is smaller and fusiform, as in Goniodoris, and the principal spermatheca is roundish and much 

 diminished in size. 



The vascular system is apparently as highly developed in Polycera as in any of the 

 DorididcB. The heart is contained within a pericardium, and is composed of a ventricle (p) 

 and an auricle ; the latter receiving the blood from the gills and skin, the former distributing- 

 it again by a large artery from the anterior apex in the usual manner. The portal heart lies 

 below the pericardium, and is rather small. In P. quadrilineata there is a folliculated glandular 

 organ in connexion with the arterial system, lying on the right side in front of the reproduc- 

 tive organs. This is similar to what has been observed in Idalia and Ancida, and will probably 

 be found in all the Polycerina. The heart beats sixty-two times in a minute in P. Lessonii ; in 

 P. ocettata, from seventy-two to eighty-eight times ; and in P. quadrilineata from ninety to a 

 hundred times. 



The renal organ is distinctly visible in P. Lessonii, and is copiously supplied with vessels ; 

 the margins have a dendritic appearance, and the external orifice is placed to the right in front 

 of the anus. In the other species this organ has been less perfectly observed. 



The nervous system is provided with three pairs of oesophageal ganglia, besides the ac- 

 cessory ones. They may all be considered as placed above the alimentary tube, though the 

 'pedials droop a little on its sides. In P. quadrilineata, the cerebroids (fig. 12, a, a) are 

 irregularly quadrilateral, inclined to pyriform, with the broad ends united across the median 

 line. They give off from the frontal margin three pairs of nerves, (2, 3, 4), which go to the 

 lips, the oral appendages, and channel of the mouth. The olfactory nerves (1) pass from the 

 upper surface of the anterior margin, and have each at their origin a small round ganglion, 

 and another {j), which is considerably larger, is connected with them as they reach the 

 laminated portion of the tentacles : from the latter, several nerves pass up the tentacles. The 

 branchial ganglia [b, b) are round, and closely adherent to the posterior extremity of the 

 cerebroids : they give off each two nerves, one (7) of which goes to the skin of the back, and 



