130 THE AMERICAN MONTHLY [May, 



the cleavage planes become filled with paraffin and are 

 thus obscured. The method is useful, however, when the 

 embryos have developed a characteristic shape or sym- 

 metry that is visible through the coating of paraffin. I 

 was still at sea with my young stages when Dr. William 

 Patten told me of a method employed by him, in exper- 

 imenting with which I developed the method which is 

 the subject of this communication. 



The method depends upon the use of paj)er having a 

 surface of raised parallel lines, or in other words, having 

 a grained or rep-surface. Writing paper of this kind is 

 made in various sorts and can be had in the market. 

 The best kind is that which is known as " linen cloth," 

 and is made in imitation of some coarse fabric. It bears 

 series of parallel raised lines intersecting one another at 

 right angles in imitation of the woof and warp of some 

 woven fabric. The surface of the paper is thus divided 

 into minute squares, the meshes representing the spaces 

 between the imitated threads of the fabric. If such 

 paper is not to be had, any paper that has a distinct 

 grain will answer, provided the lines of the grain are 

 straight and parallel. 



Cut a rectangular strip of the paper so that the cut 

 edges are parallel and perpendicular to the direction of 

 the grain (I use strips about 5xl5mm.) and paste it 

 smooth to a glass slide by means of a solution of gum- 

 arabic. The rougher side of the paper, i. e. the side 

 showing the grain more distinctly, should lie uppermost, 

 or exposed. When the gum has dried, the exposed sur- 

 face of the paper is coated with a thin film of the gum- 

 arabic solution, which is best applied with a brush. 

 When this is quite dry, the gummed surface of the paper 

 is coated with a thin layer of collodion. This should be 

 ordinary flexible collodion diluted with three parts of 

 ether, and should be applied with a small brush so as to 

 produce a very thin film. The coating of collodion 



