1818.] Philosophical Transactions for 1817 , Part II. 55 



and as it follows from this view of the subject that actual im- 

 pregnation takes place in the ovarium, many hypotheses have 

 been formed to account for the manner in which the semen can 

 pass along the Fallopian tube. The present writer, on the con- 

 trary, supposes that the corpus luteum is a compact glandular 

 substance in which the ovum is formed, and that, from certain 

 causes, it may pass into the uterus, where it is impregnated. 



The small ovum was given to Mr. Bauer, of Kew, in order 

 that he might examine it by his microscope, and we are presented 

 with a very minute account of its appearance. It is described as 

 consisting of a membrane, comparatively speaking of consider- 

 able thickness and consistence, forming a kind of bag of an oval 

 form, nearly -Jfo of an inch long, and about ^%^ of an inch 

 broad : on one side it has an elevated ridge down its longest 

 diameter, and on the other side it appears open for nearly its 

 whole length, the edges of the membrane being rolled inwards, 

 so as to give it something of the shape of a shell of the genus 

 voluta. The outer bag contained an interior smaller bag, one 

 end of which was nearly pointed, the other obtuse ; in the middle 

 it was slightly contracted, so as to leave two protuberances, 

 which, it is conjectured, were the rudiments of the heart and 

 head. These protuberances were formed by two little corpuscles, 

 which were contained in the interior bag, and were enveloped in 

 a slimy substance like honey. The paper is accompanied by 

 some characteristic engravings from Mr. Bauer's drawings. 



The object of Mr. Knight's paper on the expansion and con- 

 traction of timber is to show that this effect is principally pro- 

 duced by means of what is called the silver grain of the wood, a 

 series of cellular processes, which are extended in the form of 

 radii, from the central medulla of the tree to the bark. In a 

 paper which was inserted in the Philosophical Transactions for 

 the year 1801, he endeavoured to prove that the motion of the 

 sap depends upon the action of these processes, as they are 

 affected by the different degrees of heat and moisture to which 

 they are exposed ; and he has been confirmed in this opinion by 

 many experiments and observations, which he has had an oppor- 

 tunity of making since that period. 



The first set of experiments which he relates consisted in 

 taking thin boards of oak and ash, which were cut from the tree 

 in different directions with respect to the silver grain, " so that 

 the convergent cellular processes crossed the centre of the sur- 

 faces of some of them at right angles, and lay parallel with the 

 surfaces of others." When both these pieces of wood were 

 placed under similar circumstances, those which had been 

 formed by cutting across the convergent cellular processes soon 

 changed their form very considerably, the one side becoming 

 hollow, and the other raised ; and in drying, these contracted 

 nearly 14 per cent, relatively to their breadth. The others retained. 



