11 



single, and the branchi® serve the purpose of lungs ; the 

 water passing through the gills effecting that change in the 

 blood which is performed by the air in the lungs in the latter. 

 Among the peculiarities noticeable in the circulation of 

 these young salmon, perhaps the most interesting is that 

 we perceive in the appendage to the abdomen, termed the 

 umbilical vesicle. I should observe that the young 

 salmon immediately it is batched, possesses this strange 

 vesicle, which appears, as far as I can ascertun, to con- 

 tain a large amount of albuminous substance, and coloured 

 oil globules, and to be supplied with innumerable blood 

 vessels. In this stage of growth, the young salmon is 

 perfectly transparent, and on being placed under the 

 microscope, we may observe the entire circulating vessels, 

 the beating of the heart, and the course of the blood 

 through the system. The vertebra and viscera are also 

 easily seen. The umbilical vessel is of large size, com- 

 pared with the young fish. During its growth, this ap- 

 pendage is gradually absorbed, and at the same time 

 the different portions of the young tish as they are 

 built up, become gradually opaque. The following is the 

 result of the observations I have made during some weeks, 

 examination of these minute fish. Firstly, with regard to 

 this umbilical vesicle. All the blood with which it is 

 supplied appears to proceed from the liver, at least from an 

 organ which I suppose to represent the liver, and the 

 blood sent to this organ comes from the vena cava, 

 that great dorsal blood vessel which brings the blood back 

 to the heart after traversing the system. This blood, after 

 passing the liver, is spread over the whole umbilical vesicle 

 by a network of veins which lastly unite, towards its infe- 

 rior extremity, into large veins (vena porta), by which 

 it is conveyed to the heart. This vena porta unites with 

 the vena cava, and thence the blood enters the auricle, 

 which is placed above the ventricle, the whole organ 

 being situated in what I should terra the cervical region, 

 or between the gill openings and the body— the (ish pos- 

 sessing no neck ; or, I Hhould have said, his heart was in 

 his neck (not in his mouth). The contraction of the auricle 



