VOL. XXIII.] PHILOSOPHICAL TRANSACTIONS. 709 



In noticing the condition of the foetus in ovo of oviparous animals, the 

 author remarks that " there is at the obtuse end of the egg a small cavity 

 filled with air, which is the succedaneous instrument to the respiratory organs. 

 — Fabritius ab Aquapendente, and, after him. Dr. Harvey, have assigned divers 

 uses to this cavity or air vesicle, the extravagance of which have perhaps deterred 

 others from inquiring so much into the use, as the importance of it required. 

 But though I cannot agree to that perspiration, refrigeration, and respiration, 

 which they make it the instrument of, yet perhaps the air that was inclosed in 

 that cavity, may through the augmentation of the body of the pullus, and its 

 own rarefaction (which is at last so great as to occupy half the shell) break the 

 membrane, which separated it from the pullus, and thus give so much respi- 

 ration as to form the chirping voice, which is often heard before the breaking 

 of the shell, and with it give an addition of strength to enable it to break the 

 shell. But how it should respire sooner, is to him (he says) inconceivable." 



The Description and Manner of Using a late invented Set of small Pocket- 

 Microscopes, made by James JVilson. N° 281, p. 1241. 



The late improvements made by magnifying glasses are not so much owing 

 to the make, and. the compounding of microscopes, as to the methods of apply- 

 ing objects for the advantage of light. Experience, as well as the authority 

 of Dr. Hook,* assures us, that single magnifying glasses, when they can be 

 used, are preferable to microscopes composed of two or more magnifying 

 glasses. 



Mr. Wilson here describes all the parts of his microscopes, with references 

 to engraved figures of the same; and he describes the manner of using them, 

 in viewing different objects, with necessary cautions and directions ; such as are 

 to be found in many books expressly treating on such subjects. 



Abstract of a Letter from the Rev. Mr. Abraham De la Pryme, F. R. S. con- 

 cerning a f'Vater-Sjiout observed by him in Yorkshire. N°281,p. 1248. 



On the 15th of Aug. l687, about 2 o'clock in the afternoon, there appeared 

 a water-spout in the air, at Hatfield, in Yorkshire. It was about a mile ofF, 

 coming directly to the place where I was; upon which I took my perspective 

 glasses, and made the best observations on it I could. 



tion between the foetus and mother ; but that portion of the placenta next ihe uterus having its cells 

 filled with blood derived from the uterine arteries, a part of that blood (which is arterial or previously- 

 oxygenized) is absorbed by the radicles of the umbilical vein, and by this last, is conveyed to ihe foetus. 

 Hence ihe division uf the placenta into the uterine part and fcEtal part. 

 * In the preface to his Micrographia — Orig. 



