FIONA. 



resembles some of the Borides, particularly Boris repcmda, in which the testis has appended 

 to it, not only a vas deferens, but is likewise supplied with a much constricted duct, which 

 unites it to the oviduct as in Fiona; and the testis, too, of the Boris is very similar to the 

 same organ in this animal. 



The vascular system is very interesting, inasmuch as we have been able to trace the 

 branchio-cardiac vessels more completely than in any other member of the family. Indeed 

 nearly the whole of these vessels are distinctly visible on the skin of the back, rising above 

 the general surface, and exhibiting a very curious and novel spectacle, much resembling the 

 vascular appearance on the lateral expansions of fflysia. The heart (fig. 2 a, and fig. 10) is 

 situated about the middle of the back, where it forms a large oval swelling immediately below 

 the skin, having the generative organs beneath. From the posterior extremity of the 

 swelling, an elevated, broad, and rounded ridge, (fig. 2 d), passes down the median line of 

 the back to the termination of the body. This ridge is joined on either side by numerous 

 similarly elevated branches, (e), which divide and subdivide as they approach the cloak-like 

 expansion on the sides of the body. The whole of these branches, and their subdivisions, 

 standing boldly up from the general surface of the skin, have the branchial papillae set along 

 them, and they give off twigs, which pass up the broad membranous expansion of the 

 papillae, (fig. 3). 



On opening the heart from above, the ventricle (fig. 10 a) and auricle (c) are found to 

 occupy a well-defined oval pericardium. The ventricle is large and muscular, of an irregular 

 elliptical form, giving off the aorta (b) in front, which, in the usual manner, supplies branches 

 to the various organs. The auricle is united to it behind, a little on the left side ; it is delicate 

 in comparison with the ventricle, but is nevertheless abundantly supplied with muscular fibres ; 

 it lies diagonally in the pericardium, having the left side advanced almost to the front of that 

 organ, where it receives a trunk-vein (y) from the skin. The right side of the auricle stretches 

 backward, and receives a similar trunk- vein from the skin of this side, almost at the posterior 

 extremity of the pericardium. On laying the dorsal wall of the auricle open, its cavity is 

 found to be continuous with that of the great posterior elevated median ridge or trunk-vein 

 (d) before alluded to ; and on opening this, the various lateral branches (//,) are observed 

 debouching into it on either side. It is therefore evident that these three trunk-veins, their 

 beautiful system of ramifications all lying imbedded in the skin, are branchio-cardiac veins, 

 and herein we find a clear proof also of the branchial character of the papillae. 



The papillae (fig. 3) are, as we are already aware, of a very peculiar character in this 

 animal, being somewhat compressed, as in Eolis papillosa, and having a distinct, broad, frilled 

 membrane {b) extending up their inner margin. It is, as before remarked, from the border of 

 this membrane that the twigs of the efferent vessels are given, and they pass down its entire 

 length. When a transverse section of a papilla (fig: 9) is made, a widish canal (b) is seen to 

 pass up the opposite margin. This may be looked upon as an afferent branchial vein, and 

 deteriorated blood, passing from the skin up this canal, may be supposed to filter through the 

 cellular tissue (d), between the external skin and the glandular sheath of the papilla, and so 

 find its way to the efferent vessel (c) at the free border of the membrane. If this view be 

 correct, and it would seem scarcely possible to doubt it, the papillae are evidently specialised 

 breathing organs, and by no means so low in organisation as has been thought. 



At the same time, from the arrangement of the branchio-cardiac, or efferent vessels, and 



