PROTOPLASM OF OVA 125 



very transparent Eotifer Hydatina senta show a reticulate 

 nieshwork most distinctly after a little pressure. At the 

 same time it may be determined that the surface of the egg, 

 under the thin vitelline membrane, is formed of a layer of 

 alveoli with beautiful radial striation, which is bounded ex- 

 ternally by a very dark and fairly thick border. Strongly 

 compressed ova, of which the protoplasm is squeezed to 

 bursting, show the reticulate meshwork structure exceed- 

 ingly clearly, with strongly refracting granules, varying in 

 size from minute to much coarser ones, deposited in the 

 nodal points (Plate VII. Fig. 4). Since the protoplasm of 

 the ovum passes into a state of lively flowing movements as 

 soon as it is squeezed, it follows therefrom that it is com- 

 pletely fluid. 



Very fine sections through eggs oi Sphcerechinus granulans, 

 which have been preserved in picro-sulphuric acid and then 

 tinged brown in 1 per cent osmic acid, show the composition 



watery solution of hsematoxylin. One obtains in this way extremely 

 intense staining, varying from blue to dark brown, which is very 

 necessary for the thinnest sections (1 /j,). This method also gives certain 

 differentiations of colour. Frequently, however, in order to obtain the most 

 intense possible staining for very thin sections, aniline colours, especially 

 gentian violet in aniline water, were used. The so-called acid haematoxylin, 

 so often spoken of, is greatly diluted Delafield's hEematoxyliu, to which some 

 drops of acetic acid are added, until the colour becomes distinctly red. This 

 mixture gives especially good nuclear stains, which show in particular the 

 colour differentiations of the nuclear contents described by me above. In 

 order to prepare the thinnest sections, I cover the out surface of the objects 

 embedded in paraffin with a thin skin of celloidin before cutting them ; this 

 method succeeds very well for obtaining sections of 1 /i, or even considerably 

 thinner. The investigation of the sections was first done in water, since the 

 delicate protoplasmic structures naturally show up much more plainly in the 

 feebly refracting water than in resins or the like. For the first investigation, 

 therefore, this method is much to be recommended, although any one ex- 

 perienced in these matters can usually make out the structures in prepara- 

 tions mounted in Damar or Canada balsam also. The distinctness of the 

 images is, however, so much greater in water that the use of that medium is to 

 be strongly recommended. As has been remarked, the most intense staining 

 is scarcely sufficient in the investigation of such fine sections, the more so as 

 even with it the protoplasmic framework proper only stains extremely slightly, 

 so that strong solutions of the stains seem almost indispensable for the recog- 

 nition of such delicate structural elements. A section of about 0'5 to 1 /j. 

 through an object which after staining with iron haematoxylin appears 

 absolutely black, is yet so faintly coloured that further staining on the slide 

 is often necessary. 



