Proceedings of the Royal Society of London/Volume 2/On the Structure of the Organs of Respiration in Animals which appear to hold an intermediate Place between those of the Class Pisces and the Class Vermes, and in two Genera of the last-mentioned Class
The genera of animals here enumerated by the author, are the Lamprey, Myxine, an animal between the Lamprey and the Myxine, the Aphrodita aculeata, and the Leech.
In the Lamprey, the organs of respiration consist of separate oval bags, that have seven openings on each side of the neck, for receiving and emitting the water which they breathe by means of a cartilaginous thorax surrounding the bags. In the Lampern, which is of the same genus, the structure is very similar, but the cartilages of its thorax are weaker.
In an animal brought from the South Sea by Sir Joseph Banks, there are also the same number of external openings, and the same number of bags; but there is no cartilaginous thorax, and hence the author is induced to consider the animal intermediate between the Lamprey and Myxine, which it resembles in having teeth, and in having a mesentery to its intestines.
In the Myxine, there are only two orifices on the under surface of the neck; but these branch internally to six separate bags on each side.
In the Aphrodita aculeata, the organs of respiration differ so much from other animals of that tribe, that the author enters more minutely into the peculiarities of their structure. There are thirty-two openings between its tufts of bristles on each side, which lead to one large cavity on the back, into which project two rows of globular cells that communicate with the viscera, the use of which may admit of some doubt.
In the Leech, there are sixteen external orifices on each side under the surface of the belly, communicating with an equal number of distinct globular cells.
With respect to the respiration of the Lamprey, the author observes, that it naturally differs from that of fishes in general; for whilst they are attached by means of their mouths, the respiration could not then be carried on by means of that organ. A portion of the respired water may, however, be occasionally received into the œsophagus by a tube, with which all the bags communicate, and thence may pass into the stomach.
In the animal from the South Seas, which has no cartilaginous thorax, the respiration must be performed by the elasticity of the bags themselves.
In the Myxine, the author conceives that the water received by the two external openings is carried wholly into the œsophagus, and is then thrown out by an orifice that opens externally below those before described.
In the Aphrodita and Leech, the same openings which receive, also emit the respired water; and since in the latter the pressure of the bags is affected by the muscles of the body, their respiration must vary according to the degree of bodily exertion.