THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. IX. OCTOBER, 1888. No. 10. 



Elementary Histological Studies of the Cray-fish. — XI. 



By henry LESLIE OSBORN. 



CHAPTER IV. — THE OVARY. 



III. Histology. — (Continued from page 143.) 



2. Exafnination of fresh material. — If one v^^ould be thorough in the 

 study of the ovary he must not trust alone to sections, though from these he 

 can learn a great deal with regard to the structure of the organ under discus- 

 sion. To mount fresh material for study first break into two pieces a \ in. 

 cover-glass and lay the two halves on the centre of the slide, leaving between 

 them a small oblong compartment. This will form a cell and support the 

 cover from resting heavily upon the object — a fatal mishap should it occur. 

 This simple cell will further be open at each end for the very ready passage 

 of fluids if 3'ou wish to irrigate. After the cell is thus ready for use, snip 

 with fine sharp scissors a bit from the ovary containing a half dozen eggs,* 

 and spread it out carefully in the cell, put a drop of salt solution (see page 

 141 foot note) upon it, and then carefully lower the cover over it. If the 

 cover presses upon the eggs, which may be thicker than thin glass, build up 

 the cell with halves of a second cover-glass. With the naked eye can be 

 seen on the mounted specimen the yellow color of the eggs, and in the centre 

 of each ^'g'^ a minute, lighter-colored spot. The low power will show that 

 there are on the slide, besides the eggs with the yellow contents, numerous 

 round or oval bodies of small size, uncolored, and with a central, transpar- 

 ent spot in each. With the high power, examine in more detail all the parts 

 of the slide. 



N. B. — In studies of live eggs or of any mounts of fresh material it is best 

 to use the microscope with the stage horizontal, because of the change of field 

 in a fluid due to gravitation in a stage inclined. The slide contains two sub- 

 stances to be examined, viz., the ripe eggs and the young eggs. 



I. The ripe egg. — This is very opaque. On its border, when the lens 

 is leveled for the focal plane passing horizontally through the centre of the 

 egg, a thin translucent belt can be seen encircling the Q%^' Study of this 

 shows it to be cellular, for nuclei can be demonstrated in it. Selecting an 

 egg in which the envelope is slightly separated from the &^^ proper, use it 

 for further observation. First irrigate with dilute acetic acid (.5%), being 

 very careful not to use the acid too strong nor for too long a time. Then 

 focus up slightly above the median level of the egg and you can obtain sur- 

 face views of the envelope slightly oblique ; and here the acid will demon- 

 strate beautifully the pavement epithelium of which the o,^^ envelope is 



* I have spoken thus far, and shall continue to so speak, of the products of the ovary as eggs ; this term is a 

 convenient one to use. It must be understood that, strictly speaking, these bodies are called ovarian-eggs, and 

 that they are not as yet ready for development. 



