34 The Ottawa Naturalist. [May- 



is far more^acute than the sense of smell, as is proved by the 

 delicate structure of the ears in the hind part of the skull. But the 

 most sensitive structure in fishes is the lateral line, a series of 

 openings in the scales along each side of the body. Tempera- 

 ture, water pollutions and other external conditions, affect the 

 lateral line, the microscopic structure of which shows that its 

 importance has apparently been over-looked by naturalists. The 

 brain is of the simplest kind, merely six rounded lumps or lobes, 

 the first pair'being the olfactory lobes, the second the optic, and 

 the third the cerebral hemispheres, which are very small. The 

 optic lobes, whence spring the nerves of sight, are by far the 

 largest. Behind all is the cerebellum, which continues into the 

 spinal cord. The eggs, larval condition, and other interesting 

 features, were detailed in the concluding part of the lecture. 



II. "A Bird."— In contrast with the fish, Professor Prince 

 drew attention in his second lecture to the skull of the bird, 

 which in the adult is very compact and soldered together, 

 whereas in the early stages the bones (or cartilages) are separate, 

 like the separate elements in the fish's skull. A single knob or 

 joint, called the occipital condyle, projects from the back of the 

 skull and unites it to the atlas or first joint of the neck. The 

 fore-limb is not a fin, but a wing consisting of two fingers and a 

 thumb. In the penguins the wings are used as fins for swim- 

 ming and bear scale-like feathers. The heart is four-chambered 

 and one great artery (the right aortic arch) carries the blood all 

 over the body. Two pulmonary arteries carry blood from the 

 right ventricle to the lungs. The lungs open by air-tubes into 

 large sacs, which often penetrate the bones and increase the 

 buoyancy of the body. The ribs of birds bear projections called 

 uncinate processes, which are also found in reptiles. Birds and 

 reptiles have many points in common. The concluding part of 

 the lecture dealt with the eqg and the embryonic development 

 of a bird. The growth of the skeleton, of the feathers, &c., was 

 described in full detail. 



III. "A Four-footed Animal" formed the subject of 

 the last lecture, and it was shown that the complex structure of 

 mammals, or highest animals, admitted of a description of only 



