NOWLIN : THE VITELLINE BODY IN SPIDER EGGS. 291 



Certain groups of the cells lining the tube enlarge slightly and 

 in time can be recognized as early oogonia. There are usually 

 ten or twelve of the young germ-cells found clustered together, 

 while around them the epithelium is unchanged. In one ovary 

 such bunches may be very numerous. I shall not here describe 

 the process in detail, but merely show how this change brings 

 about the change in the form of the ovary. As these small 

 germ-cells grow they push out through the muscular wall (PI. 

 XII, fig. 6) , causing numerous diverticula on the outside of the 

 tube. Projecting thus may be found oocytes of nearly all ages, 

 some very young, just pushing to the surface ; others almost 

 mature. By the time several generations of these cells have 

 formed their follicles, the tube has become much distorted in 

 shape. The walls in the old ovary are so convoluted that the 

 lumen is difficult to distinguish. This is due to the great 

 growth of the walls as well as to the distorting influence just 

 mentioned. 



For a study of the morphology of the ovary a young speci- 

 men is much better than an old one. The ovary has more 

 rigidity at this time and is a straight tube, of which it is very 

 easy to obtain a longitudinal section. A study of the organs in 

 situ is perhaps more satisfactory than any other way, giving us 

 best their relation to each other in the body. Fleming is very 

 good as a fixative for this purpose, since it will penetrate even 

 the tough outer covering of the body. The surest way is, how- 

 ever, to remove this covering before placing the fluid upon it. 

 The fixative will then readily penetrate the tissue of the liver 

 and will fix the ovary perfectly. 



There is another advantage, too, in working with the young 

 ovary. The ovarian cells and those in the follicles have not 

 differed to any extent physiologically, and all come out equally 

 well preserved. In the mature ovary, those eggs which have 

 becme filled with yolk take the stains so differently from the 

 younger eggs, especially the cells of the ovarian wall, that in 

 preparation one set must be completely sacrificed for the other. 

 It is almost impossible to make longisections of the distorted 

 adult ovary. Cross and oblique sections quite as often occur, 

 producing some very confusing images to one unacquainted 

 with the structure of these organs. 



