IV. 



Some Useful Methods in Microscopy. 



HAVING been occupied during the spring of 1892 in studying 

 the early stages in the development of Loligo and Sepia at 

 Naples, I found myself unable to make any progress in solving the 

 problems presented by these difificult objects until I had obtained a 

 satisfactory method of preparing and mounting blastoderms, quite 

 freed from yolk, for study of surface-views under the microscope. 

 After trying many methods, I at last hit upon one which, while 

 exceedingly simple in application, not only gave the most beautiful 

 results for these blastoderms, but has also proved applicable for 

 other objects which are not more than a few cell-layers in thickness, 

 such as early chick embryos, and still more so, of course, for 

 unicellular objects, such as Protozoa. It seemed to me, therefore, 

 desirable to describe briefly the methods employed by me, since they 

 may prove useful to other zoologists. In so doing, however, I do not 

 in any way wish to lay claim to any originality or precedence in 

 inventing them. For all I know they may have been already 

 described by many other investigators. Wherever I give any 

 method which I have obtained from an author I shall give the 

 reference to him ; where I do not do so, my apparent oversight is 

 to be set down to my ignorance of the now vast literature of the 

 subject. 



The method employed by me for cephalopod blastoderms is 

 exceedingly simple in principle, though its mode of application varies, 

 of course, with the nature of the object, and may require a high 

 degree of manual skill, to be obtained only by much practice. It is 

 as follows. The fresh objects are first brought into Hermann's fluid 

 for a short time, until all the cells are fixed ; this is, as a rule, effected 

 in 2-5 minutes, but the proper length of exposure to the action of the 

 reagent can best be determined by the eye ; as soon as the cells 

 become white and opaque they are sufficiently fixed. Too long 

 exposure is injurious to subsequent staining. 



After the Hermann's fluid, the objects are carefully washed in 

 two or three changes of water to extract all the reagent. This also 

 is an important point for staining. After washing, the objects come into 

 either alum carmine or Paul Mayer's^ newly invented stain carm-alum. 



1 " Ueber das Farben mit Carmin, Cochenille, und Hamatein-Thonerde." 

 Mitth. Zool. Stat. Neapel. Bd. x., Heft. 3, p. 489. 



