PKOGRESS OF MICROSCOPICAL SCIENCE. 35 



puscles in tlie neiglibourliood of the blood-vessels. On observing 

 carefully for some time the border of the exposed cerium, the colour- 

 less corpuscles which have emigrated from the blood-vessels nearest to 

 the edge are readily seen to migrate, with very active amoeboid move- 

 ments, to the edge, where they rise gradually, one after the other, 

 freely to the surface. After a certain time isolated groups of colour- 

 less corpuscles are found on the free surface of the edge of the corium, 

 performing lively movements. Soon, however, they become flat, sharply 

 outlined, their protoplasm transparent, and their nuclei less marked. 

 Two or three hom-s afterwards the whole edge of the corium is covered 

 with one layer of such cells. After the whole defect of the epithelium 

 is filled up by that layer, the cells become again less sharply outlined, 

 and the corium seems to be covered by a homogeneous substance in 

 which nuclei become visible, gradually progressing from the peripheral 

 parts towards the centre. In the course of the following hours, below 

 that layer a second one is formed by emigrated colouidess corpuscles, 

 and then a third one ; at the same time the cells of the layer first 

 formed enlarge, become more stiff and flat. Isolated cells are always 

 seen to migrate from the depth towards the free surface through those 

 layers. After twenty-foiu' hours the defect is filled by several layers 

 of cells, the thickness of the layers being generally greater than that 

 of the old epithelium in the neighbourhood, as the cells of the new 

 epithelium are softer and less flattened than the cells of the former. 

 Between the cells of the new-formed epithelium pigment-cells make 

 their appearance. These originate from two sources : first, from the 

 branched pigment-cells that are to be found generally in the epithe- 

 lium of the web ; and, secondly, from the pigment-cells of the corium. 

 As regards the first source, it is to be noticed, according to Biesiadecki, 

 that the interepithelial branched pigment-cells of the neighbourhood 

 of the defect become amceboid, undergo division, and while some of 

 their offsprings remain amongst the cells of the old epithelium, some 

 other ones migrate away between the cells of the new-formed eiDithe- 

 lium. Biesiadecki takes it as probable that pigment-cells which are 

 to be found lying round the blood-vessels of the corium become also 

 amoeboid, and migrate towards the surface between the cells of the 

 new epithelium. Two important facts are still to be mentioned re- 

 lating to the regeneration of the ei^ithelium. First, if in the forma- 

 tion of the blister, the deepest layer of the rete Malj)ighii be left on 

 the corium, that layer, after the removal of the blister, is generally 

 raised and removed by the subsequent exudation. Secondly, the old 

 epithelial cells in the immediate neighbourhood of the defect do not 

 undergo any active changes. These two points stand in very sharp 

 contrast to the doctrine commonly held ; namely, that in the j)rocess 

 of regeneration of epithelium, the new-formed epithelial cells are 

 the result of proliferation of the deejiest epithelial cells which have 

 been left, or of those which border the defect. — The Medical Becord, 

 April, 1873. 



The Mode of Fertilization in the Grasses. — An American wi-iter says 

 that Professor Hildebrand, of Freiburg, recently made to the Berlin 

 Academy a detailed communication on this subject. He shows that 



