the shape of the remainder of the fish bore a strong resemblance to that of a fiddle, the tail of the gasterosteus answering to the fingerboard and head of the instrument. But the sketch (Plate XLIII. Fig. 1) will afford the best idea of their figure, as seen by looking down upon them from above when swimming about in the vessel which contained them. In order to ascertain the cause of their extraordinary malconformation, several of them were subjected to immediate dissection, when from three to, in some cases, seven or eight white worms, the tænia solida of Gmelin (vid. p. 3079), were found in each individual. Neither roe nor milt could be discovered in any of these diseased sticklebacks; though in the others brought in at the same time, which were healthy and properly shaped, and which upon dissection were found free from tæniæ, either the lactes or ovarium in complete perfection was invariably found. In order to submit them to further observation, and for the purpose of watching how the disease would terminate, three of the fiddle-shaped sticklebacks were preserved alive in a soup-plate full of water, which was carefully changed every morning. These fish were regularly supplied with a number of live red worms from the same pond, about six or seven-eighths of an inch in length: these were the nais digitata of Gmelin (vid. p. 3121), of which each of them ate three or four every day. All this time they were perfectly lively and active, and were frequently observed fighting with each othe for the small worms on which they fed. About a fortnight after they were put into the plate, one of them by some accident sprung out of it, and in the morning was found dead near it on the frame on which it stood. Upon its being dissected, two tæniæ were discovered in it. The two sticklebacks which remained continued in their usual state of activity until about the middle of October, when one of them began to appear indolent and feeble, and at last, towards the end of the same month, was one morning found dead, and four tæniæ of the length of from an inch and an half to rather more than two inches, which had been discharged from its body, were observed in the plate near it. The third gasterosteus now began to show symptoms of dwining, and on the morning of the 7th of the present month (Nov.) it died in the same way as the last had done. Having all along taken much interest in the fate of these fish, Mr. Brodie, to whom I had accidentally promised a visit on that day, ordered the plate and its contents to be preserved as it was until I should see it. On examining the dead stickleback, which was about an inch and an half in length, I observed small globular pustules on one or two different parts of its body. Three tæniæ were lying in the plate beside it, and the aperture of the anus was so much enlarged and lacerated as to leave no doubt that the worms had forced their way out at that place. The taniæ were above two inches in length by about the fourth of an inch in breadth, perfectly white, flat, and formed, like other tape-worms, of a number of rings. Their shape was smaller towards the head; but the other extremity terminated more bluntly, being of the same

breadth as the rest of the body, until the rings suddenly contracted to a point. They were still alive, and one of the largest, which had been left nearest to the dead fish at the time they were examined in the morning, had again before evening partially insinuated its head into the aperture from whence it had originally escaped.

Having expressed a desire to examine the general state of the sticklebacks then at large in the same pond from which the others had been taken, a servant was dispatched, who soon returned with several of them in a vessel of water. On examination, these were all found to be in the diseased state, all, of them presenting the same uncouth, fiddle-shaped, appearance. They were all affected too in some degree by the same sort of globular pustules which have just been described as remarked on the dead one. Each fish had from one to three or four of these pustules, some of them on the body of the animal in different situations, and many of them were noticed on the fins, and even on the delicately webbed extremities of these members. The figure above referred to is a just, though rude, representation of one of the most tumid of these fish, and three of the little pustules in question may be observed distinctly marked on it. Having put one of these fish to death by decapitation, I proceeded to dissect it with a pair of fine pointed scissars, beginning at the anus, and cutting upwards through the bony cartilage of which the belly of the gasterosteus is composed. On laying open the cavity of the abdomen, the tæniæ were immediately discovered, not in the intestines, but immediately beneath the peritoneum. The whole cavity was so stuffed with these worms, that as the fish lay on its back, the alimentary canal and all the other intestines were completely covered and hid by them. The tæniæ appeared to lie with their heads towards one another in the centre, and having their other extremities folded or rolled up in the anterior and posterior regions of the cavity, so as to form the double protuberance so distinctly visible in the external appearance of the fish when alive. The tæniæ, which were above an inch in length, and four in number, were perfectly lively when removed from their situation. One of the globular pustules figured in the sketch was now subjected to minute dissection under the microscope, when it was found to be merely a diseased sack, formed by a distension of the skin of the fish, of the colour and spots of which it partook according to its situation on the body of the animal; having the neck which attached it to the rest of the skin extremely slender. When opened, it was found to contain a whitish coloured, and rather viscid, pus. It is probable that these pustules were merely attendant symptoms of the diseased state of the sticklebacks.

It would seem from the circumstances just detailed that as soon as the gasterosteus aculeatus has provided for the continuation of its kind, by depositing or impregnating its ova, it is immediately doomed to a gradual destruction by the tænia solida, with which it then begins to be internally infested. And if this fact be established, and the connexion between the time of spawning and that

of the commencement of the disease shall be found to be invariable, it will present one of the most curious, amongst the many, provisions of nature hitherto noticed, for preventing the too great accumulation of a particular species. I may also remark that the particular situation in which the tæniá solida is found in the gasterosteus aculeatus may perhaps in some degree tend to support Dr. Chisholm's theory of the propagation of some worms hinted at in his paper on the malis dracunculus, or Guinea worm, in the 42d number of the Edinburgh Medical and Surgical Journal.

I remain, Sir, your obedient humble servant,
THOMAS LAuder Dick.

ARTICLE VI.

Letter to Dr. Wells respecting Dew, from Professor Prevost, of Geneva.

SIR,

I HAVE but just had an opportunity of perusing your letter to Dr. Thomson, published in the April number of the Annals of Philosophy for 1815, which relates entirely to Dr. Young's criticism on your work on Dew. I had some time before read your letter in the November number of the same journal for 1815, in which you answer the request which I had made you for an explanation relative to the experiments of M. Benedict Prevost on the water deposited from the air.

1. On reading this last letter, and before I had seen the preceding one, I thought I saw very clearly that you considered it as impossible for water to be deposited on the outside of panes of glass when the external air is colder than the internal; but as M. Benedict Prevost affirms very positively that water is very frequently deposited under such circumstances, I immediately requested of this philosopher his proofs, conceiving myself unconnected with the dispute, because it can be decided only by experiment, theory being unable to affirm any thing, either on one side or the other.

But after reading your letter in which you discuss the criticisms of Dr. T. Young, I thought I perceived an agreement between us, not only respecting the facts, but likewise the explanation of them.

Respecting the Facts.-M. Benedict Prevost says that "dew is often deposited on the outside of glass panes when the external air is colder than the internal." Dr. Wells does not seem to deny this fact. He appears only to say "that the body on which the dew is deposited is colder than the air from which it is deposited," *—an assertion that may be reconciled with that of M. Benedict Prevost.

*In the letter on dew in the Annals of Philosophy for April, Dr. Wells quotes