805 



SIREN. 



SIREN. 



8C6 



John Hunter, in 1766, gave the following accurate and interesting 

 description of the twofold respiratory apparatus of the Siren : " On 

 the posterior and lateral parts of the mouth are three openings on 

 each side ; these are similar to the slits of the gills in fish, but the 

 partitions do not resemble gills ou their outer edges, for they have 

 not the comb-like structure. Above and close to the extremity of each 

 of these openings, externally, so many processes arise, the anterior the 

 smallest, the posterior the longest ; their interior and inferior edges 

 and extremity are serrated, or formed into fimbri:e : these processes 

 fold down and cover the slits externally, and would seem to answer 

 the purposes of the comb-like part of the gill in fish. At the root of 

 the tongue, nearly as far back as these openings reach, the trachea 

 begins, much ia the same manner as in birds. It passes backwards 

 above the heart, and there divides into two branches, one going to 

 each lobe of the lungs. The lungs are two long bags, one on each 

 side, which begin just behind the heart, and pass back through the 

 whole length of the abdomen, nearly as far as the anus. They are 

 largest in the middle, and honeycombed on their internal surface 

 through their whole length." (' Phil. Trans.,' Ivi., 1766.) 



In the Museum of the Royal College of Surgeons in London this 

 part of the organisation of the Siren is well illustrated. 



John Hunter describes the heart of the Siren as consisting of one 

 auricle and ventricle. " What answers," says Hunter, " to the inferior 

 vena cava, passes forwards above, but in a sulcus of the liver, and 

 opens into a bag similar to the pericardium : this bag surrounds the 

 heart and aorta as the pericardium does in other animals ; from this 

 there is au opening into a vein which lies above and upon the left of 

 the auricle, which vein seems to receive the blood from the lungs, 

 gills, and head, is analogous to the superior vena cava, and opens into 

 the auricle which ia upon the left ventricle. The aorta goes out, 

 passing for a little way in a loose spiral turn, then becomes straight, 

 where it seems to be muscular : at this part the branches go off, 

 between which there is a rising within the area of the aorta like a 

 bird's tongue, with its tip turned towards the heart. This account of 

 the venso cava; opening into the cavity of the pericardium may appeal- 

 incredible ; and it might be supposed that, in the natural state of the 

 parts, there is a canal of communication going from one cava to 

 the other, which, being broken or nipped through in the act of catching 

 or killing the animal, would give the appearance above described. I 

 can only say that the appearances were what have been described in 

 three different subjects which I have dissected, and in all of them the 

 pericardium was full of coagulated blood. But besides the smallness 

 of the subjects, it may be observed that they had been long preserved 

 in spirits, which made them more unfit for anatomical inquiries. 

 They had been in my possession above seven years." (' Phil. Trans.,' 

 Ivi., 1766.) 



The structure of the heart and other organs of this interesting 

 animal, are illustrated in the preparations in the Museum of thu 

 Royal College of Surgeons of England. 



The following remarks on the blood of the Siren, by Professor 

 Owen, were published originally in the ' Penny Cyclopaedia :' 



" Among the important generalisations which the numerous obser- 

 vations of recent microscopical anatomists have enabled the physiolo- 

 gist to establish respecting the form and size of the blood-discs in 

 different classes of animals, the most interesting seems to be that 

 which Professor Wagner has enunciated respecting the relation of the 

 magnitude of the blood-disc to the persistence of tho branchial appa- 

 ratus in the Batrachian order of reptiles, on the occasion of his descrip- 

 tion of the blood-discs of the Protein angulnus. 



"The absolute size of these particles in that Pcrennibranchiate 

 Reptile, in which they may be distinguished by the naked eye, renders 

 them peculiarly adapted for minute investigations into the structure 

 of the nucleus and capsule of the blood-disc : but the value of the 

 relation between their size and the persistency of the external gills 

 must depend upon the correspondence of other perennibranchiate 

 reptiles with the Proteus in this respect. The superior size of the 

 blood-disci! of the Newts to those of the Land-Salamanders and Tailless 

 Batrachians has been confirmed by Professor Van der Hoeven's obser- 

 vations on the blood-discs of the gigantic Newt of Japan [SIEBOLDTIA], 

 of which a fine specimen has been for several years kept alivo at Leyden 

 [AMPHIBIA] ; and I have been able to add another instance of the still 

 greater relative size of the blood-discs in the Perennibranchiate Reptiles 

 by the examination of those of the largest existing species of that 

 family, the .Siren lacertina, of which a specimen, twenty inches in 

 length, is now (October 15th, 18-11) living at the Zoological Gardens. 

 The blood was obtained from one of the external gills, and immediately 

 subjected to examination. The blood-discs presented the elliptical 

 form which hitherto, without exception, has been found to prevail 

 among the air-breathing oviparous vertebrated animals : the ellipse 

 was not quite regular in all the blood-discs ; several were sub-ovate, 

 a few slightly reuiform and thicker at the more convex side : all were 

 as compressed, or disc-shaped, as in other Batrachians, with the nucleus 

 slightly projecting from each of the flattened surfaces. 



" The nucleus did not partake iu the same degree with these 

 varieties of form, but maintained a more regular elliptical form; the 

 varieties in question appearing to depend on pressure acting upon the 

 capsule and the coloured fluid surrounding the nucleus. Yet when 

 the ellipse of tho blood-disc was, as it happened in a few cases to be, 



longer and narrower than the average, the form of the nucleus pre- 

 sented a similar modification of size. 



" The following is a table of the averages of many admeasurements 

 of these blood-discs, made with tho screw-micrometer : 



" Long diameter . 

 Short diameter 

 Long diameter of nucleus . 

 Short diameter of ditto . 

 Thickness of ditto 



English inch. 

 1-4 50th 



l-S50th to l-S70th 

 1-lOOOth 

 l-2000th 

 l-3300th 



(As viewed edgeways covered by the capsule.) 

 " The nucleus was circumscribed by a double Hue, the outer ona 

 more regular than the inner one, which appeared creuated. This 

 appearance was due to the structure of the nucleus, or tho contents 

 of the nucleolar capsule, which was indicated by the outer line. These 

 contents consisted, in every blood-disc examined, of a number of 

 moderately bright spherical nucleoli, sufficiently distinct to be counter!, 

 when viewed by a Powell's l-10th inch objective, with the eye-piece, 

 magnifying 700 linear diameters : the ordinary number of nucleoU 

 seen in one plane or focus being from twenty to thirty, the total 

 number was of course much greater. The facility as well as certainty 

 of the demonstration of such a structure in a good microscope of tho 

 present day will be readily admitted, when it is remerubereil that the 

 nucleus of the blood-disc of the Siren is three times the size of the 

 entire human blood-disc. These tuberculate nuclei, when removed 

 from the 'capsule, were colourless ; the component granules or cells 

 have a high refracting power : viewed in situ they present a tinge, 

 of colour lighter than that of the surrounding fluid, and dependent 

 upon the thin layer of that fluid interposed between the nucleus and 

 the capsule. 



" The external capsule of the blood-disc is smooth, moderately 

 resisting, elastic, as was easily seen by the flattening of the parts of 

 two blood-discs that might come iu contact, and the recovery of form 

 when they were floated apart. 



" As the fluid contents of the bloo;l-disc iu part evaporated during 

 the process of desiccatiou, the capsule fell into folds iu the interspace 

 between the nucleus and the outer contour, these folds generally taking 

 the direction of straight lines, three to seven iu number, radiating 

 from the nucleus." (R. Owen, Sept. 25, 1841.) 



Blood-discs of Man and Siren, drawn by the camera lucida under a magnifying 

 power of 700 linear dimensions. 



o, Human blood-discs ; a', ditto viewed edgewise ; I, Siren's blood-disc ; &', 

 ditto viewed edgewise; c, folds of external capsule, produced by desiccation; 

 </, capsule of nucleus ; c, nucleoli. 



Siren lacertina grows to tho length of three feet; its colour ia 

 blackish. The feet have four toes, and the tail is compressed into an 

 obtuse fin. 



This Siren inhabits the marshy grounds of Carolina, especially those 

 where rice is cultivated. It lives in the mud, from whence it makes 

 excursions, sometimes on laud and sometimes iu the water. From the 

 swampy places by the sides of pools and under the overhanging trunks 

 of old trees, where it is found, it was called by the inhabitants ' the 

 Mud Iguana.' Garden was of opinion that it feeds on serpents, and 

 that it uttered a cry similar to that of a young duck ; but Barton 

 contests these statements. Its food is generally believed to consist of 

 earth-worms, insects, &c. Specimens have been occasionally kept in 

 the Zoological Gardens, Regent's Park. Quo iu 1841 was kept in a 

 vessel of pond-water with a deep bottom of mud, in which it used to 

 hide itself. It was twenty inches long, as large as the wrist of a stout 

 child of six months old, and very eel-like in its movements imd appear- 

 ance. About a dozen and a half of earth-worms were supplied to it as 

 food every other day. 



<$'. striata is blackish, with two longitudinal yellow stripes on each 

 side ; has only three toes on each foot, and is about nine inches in 

 length. 



