CIRCULATING SYSTEM.
Blood of the Ornithorhynchus.—A Mammal presenting such striking resemblances in cer tain parts of its organization to the oviparous modification of the Vertebrate type as does the Ornithorhynchus, is one of which it was obviously most interesting to ascertain the form of the blood-discs. I have made appli cations to different professional and zoological correspondents in Australia on this subject, for the transmission of a portion of recently drawn blood thinly spread and dried on glass, or preserved in its fluid state in brine and other menstrua of the same density as serum, and for the results of observations on the blood-discs of both the Ornithorhynchus and Echidna. Mr. Hobson, of Ilobart Town, Van Diemen's Land, an accomplished sur geon and comparative anatomist, has made the required observations on the blood of the Ornithorhynchus, of which lie has trans mitted to me the following account :—" The globules of the blood of the Ornithorhyn chus are discoid, and measured about the of an inch, calculating two-and-a-half millimetres to the line. The human blood globules were placed side by side with those of the Ornithorhynchus, and both in shape and size so nearly resembled each other that it was impossible to say which was human and which was Ornithorhynchus. These examinations were made in the presence of Mr. Ronald Gunn, by means of one of Oberhauser's mi croscopes; the powers used were 250, 400, and 800. In order to be sure that there was no delusion, I placed the elliptical globules of a Lizard's blood beside those of the Ornitho rhynchus. The tenacity and high florid colour of the blood, together with the greater propor tional number of globules in a given quantity" (in the Ornithorhynchus) " is most interesting in an analogical point of view." From the preceding highly valuable observa tions we may infer that the Ornithorhynrhus resembles the 111ammalia in the circular form, the size, the proportional number, and florid colour of its blood-discs, which correspond in size with those of the only Edentate species yet examined, viz. the Armadillo,* and conse quently with those of the Quadrnmana and of Man.
The blood-discs of the Echidna, according to the observations made by Dr. John Davy on a portion of blood of that animal, transmitted to England in brine, are likewise circular.
Ileart.—The heart of the Ornithorhynchus (fig. 187, a, 1), c) presents a rounded oblong form ; it is situated in the middle of the ante rior part of the chest, parallel with the axis of the cavity. It is inclosed in a thin subtrans parent but strong pericardium.
The right auricle (b) is larger and longer than the left; its appendix is free and is slightly bifid, as in the Marsupials. It receives the venous blood, also, as in that order, by three great veins; the left vena innominata (f) de scending behind the left auricle to join the termination of the inferior cave (1). The coro nary vein also terminates in the auricle to the right of the inferior cava. The right superior cave (e) is joined to the left by a transverse branch (g). AIeckel found in the heart of both the Ornithorhynchi dissected by him a deep but closed fossa ovalis, near the upper extremity of the septum. This structure would indicate that the intrauterine existence of the young was of longer duration than in the Alarsupialia.
The right ventricle (a) is capacious, with thin parietes. The tricuspid valve I found to consist of two membranous and two fleshy portions : the smallest of the latter was situated nearest the origin of the pulmonary artery, and seemed to correspond with the lesser fleshy valve observ able in the heart of certain birds, as the Ostrich; it is attached to the whole of the side of the first or adjoining membranous portion. The second fleshy portion may be described as ana logous to the muscular valve in the Bird's heart, if the lateral margin of this were detached from the wall of the ventricle, and the connection of its two extremities was preserved, the one to the angle between the fixed and moveable wall of the ventricle, the other to the auriculo-ven tricular orifice. The two edges of the lower half of the second fleshy portion of the valve in the Ornithorhynchus are free ; but those of the upper half are attached to the two mem branous portions of the tricuspid valve ; the margin of the membranous part of the valve is attached to the fixed wall of the ventricle by two small chords tendinew; and the structure of the valve thus offers an interesting transi tional state between that of the Mammal arid that of the Bird.* The origin of the pulmonary artery is pro vided with the three usual sigmoid valves.