FIONA. 



from their elevation above the general surface of the skin, thus exposing to the influence of the sur- 

 rounding medium nearly three fourths of their circumference, it is pretty clear thatthe dorsal skin 

 itself must act, to some extent, as a gill, especially when we consider further, that the whole of the 

 blood returned to the heart does not pass through the papillae : much of it, no doubt, circu- 

 lating in the spongy tissue of the skin, passes at once into the efferent vessels : and, indeed, 

 small orifices for this purpose are seen in the wall of the great median trunk- vein. Here, 

 then, as in Doris, the blood is partly aerated in specialised breathing organs and partly in 

 the skin. 



In connexion with the vascular system, Fiona is provided with an additional propelling 

 organ similar to what, in Boris, we have called a portal heart. As in that genus, this propelling 

 organ (fig. 10 e) lies below the floor of the pericardium, and, in like manner, opens into that 

 organ. In this species it is considerably elongated, with the ends rounded, and is placed far 

 back on the right side of the pericardium. It is firmly attached to the skin of the body, and 

 is internally longitudinally plicated. Judging from our knowledge of this heart in the Borides, it 

 may be supposed to throw venous blood from the pericardial cavity to the glands of the 

 papillae. Tn Fiona, it is certainly connected with the skin, and probably has some relationship 

 to the vascular apparatus therein. 



A renal organ also probably exists, though we have failed to detect it. A small distinct 

 orifice (fig. 2 b), however, opens externally immediately above the anus, and close to the poste- 

 rior border of the heart. There can be little doubt that this is of the same nature as the 

 minute opening by the side of the anus in Boris, and which, in that genus, leads into an ex- 

 tensive renal apparatus.* 



The cerebral ganglia of the nervous system resemble those of Boris, rather than of Folis. 

 They are placed at the commencement of the gullet : there are, as usual, three pairs of princi- 

 pal oesophageal ganglia, though, at first sight, only two are apparent, — the cerebroid 

 (fig. 1 1, a. a,) and branchial [b) being completely fused, forming two oval masses, resting upon 

 the upper surface of the gullet, one on each side of the median line, across which they are 

 united at the anterior extremity by a short but distinct commissure : their posterior extremities 

 diverge, and are slightly bilobed, marking the boundaries of the two ganglia of which each 

 mass is composed, — the anterior lobe indicating the cerebroid, the posterior the branchial. 

 The pedial ganglia (c, c), are irregularly rounded, being equal in bulk to the cerebr'oid and 

 branchial together. They lie against the sides of the gullet, and are united to the under 

 surface of the central masses. Besides these there is a pair of accessory ganglia, — the 

 olfactory id, d). 



The buccal ganglia, (e,e), are placed in the usual situation on the buccal mass below the 

 gullet. These are scarcely larger than the olfactory, and are of an oval form, with their inner 

 e xtremities connected across the median line by a short commissure ; their outer extremities 

 receive a cord (g), of communication from each of the cerebroid ganglia. Two minute 

 elliptical, gastro-oesophageal ganglia (/",/), are almost sessile on the anterior border of the 

 buccal. Thus, in all, there are six pairs of ganglia ; four above the gullet — the oesophageal ; 

 and two below it — the buccal. 



* Since the publication of our anatomy of Eolis, we have detected a portal heart and renal 

 orifice in that genus. 



