The Intellectual Observer

perpendicular position over the moving vessel, which steamed along under this strange canopy, and looked as though she bore a gigantic palm tree whose top reached the skies.

If the reader can imagine the emission of smoke to be intermittent instead of continuous, it is obvious that this expanding column would be broken up into rings, the constantly enlarging circular form of which would be due to the same cause as that which produces the enlargement of the column, namely, the greater pressure of the air in the centre. That this is the case will be evident on a close inspection of a single ring, when it will be found to consist of a vast number of rapidly rotating circles, arranged on a circular axis. Let the reader imagine a number of common circular bone button moulds, each with a single hole through its centre, strung on a piece of wire, which is then bent in a circular form: this would give a correct idea of the structure of a smoke-ring; and if we imagine further each of these bone moulds rotating downwards and inwards, as the ring rises and expands, the resemblance would be still more complete.

RESPIRATORY ORGANS OF THE TADPOLE.

WE have received the following interesting communication from Mr. Whitney, to whose researches on the tadpole microscopic anatomists are much indebted. Although investigations of this kind present many difficulties, the objects are fortunately plentiful, and the changes they undergo may, within certain limits, be postponed at the pleasure of the operator, who can place the tadpoles under more or less stimulating circumstances of food, temperature, etc. We have no doubt many of our readers will pursue the inquiry opened for them by Mr. Whitney, and we shall hope to give them an early account of the result of the labours in which he is at present engaged.

"In the last number of your Journal there appears an article "On the Examination of Tadpoles,' in which the writer alludes to, and extracts from, a paper of mine published in the Microscopical Journal for January, 1862. In justice to your readers, therefore, I feel called upon to explain that the organs described in my paper as 'lungs' are not indeed the true lungs (meaning the organs adapted to purely atmospheric respiration), but the internal or secondary gills. The true lungs succeed to these.

"In some of our standard works on Comparative Physiology, the existence of two separate and distinct pairs of gills (the one succeeding the other), during the metamorphosis of the Tadpole, is neither expressed nor implied. Having taken one of these

works as a guide in the commencement of my investigation, I was led into the belief that the organs which succeed to the disappearance of the external or primary gills are lungs. This supposition was strengthened by observing that the Tadpole may be frequently seen at the surface of the water, rapidly opening and shutting its mouth as if in the act of swallowing In the course of investigation, however, I arrived at the correction of this error by discovering a pair of minute tubular sacs, placed abdominally directly below the heart, behind the intestine, and united at their upper and open extremities. These are the true lungs of the future frog, in their incipient, undeveloped state.

"There are, therefore, three sets of respiratory organs, the development and vascular arrangements of which, as they appear, exist, and disappear in succession, are most interesting and beautiful-most interesting to watch, most beautiful to see, but by no means easy to investigate.

"Should the writer be enabled to accomplish the task he has proposed to himself, and is now labouring to complete, he may have the opportunity of presenting an illustrated view of the transitional changes in the vascular system which accompany the several stages of this striking and beautiful metamorphosis.

"In referring to the paper which appeared in the Microscopical Journal, it will now be understood that the organs there designated lungs' are the secondary, or 'internal gills,' and that the blood circulating in them is aerated by the oxygen contained in the water that visits them. "W. U. WHITNEY. "13, Great College Street, Westminster, April 11th, 1863."

RESULTS OF METEOROLOGICAL OBSERVATIONS MADE AT THE
KEW OBSERVATORY.