SPERMOPHILUS TRIDECEMLINEATUS MITCH. 421 



portion of that horn and would -unquestionably have caused the death of the mother. 

 The mortality of old and young from a variety of causes must be enormous, as the 

 number of adults does not materially increase from year to year. 



2. Methods. Most of the material was obtained by shooting with a small rifle. 

 The body was opened at once, and, cutting through the vagina and mesometrium, 

 the whole uterus, oviducts, and ovaries were removed and transferred to a jar of 

 fixing-solution. A careful record of each individual was kept. Upon returning to 

 the laboratory the day's collection was again examined and dealt with according 

 to the technique required in each case. Zenker's fluid penetrates easily, causes 

 little shrinkage, gives good results with a variety of stains, and is extremely 

 satisfactory in fixing the specimens. Picro-sulphuric acid, Hermann's fluid, and 

 other fluids were also used with good results. 



The exact age of any embryo not being ascertainable, all the uteri far enough 

 advanced to show swellings visible to the eye were carefully separated and classified 

 according to the size of the uterine segments. In early stages the segments are 

 practically spherical, later they become oval, arid then oblong. These were 

 calipered and arranged in stages with a variation of a half to one millimetre in 

 diameter to each stage. It is interesting to note that segments from different years 

 and various uteri when grouped in this way were found on sectioning to be very 

 similar in their development; consequently little difficulty has been experienced in 

 tracing the transition from stage to stage after the gaps had been filled by repeated 

 collections. Some forty stages were thus made by measurement, and a large number 

 of series of each stage are now in the reference collection. 



The segments were sketched, dehydrated, carried into cedar oil, then into xylol- 

 paraffine, then into soft paraffine in the oven, then into hard paraffine, and finally em- 

 bedded. While in the soft paraffine the dish containing the segment was connected 

 with an exhaust-pump and the air carefully removed from all cavities in the seg- 

 ment ; this is very essential in getting a good infiltration. The blocks were sectioned in 

 various planes; the ribbon was placed on an albumenized slide, a few drops of distilled 

 water added, flattened on a hot table, dried, stained on the slide (unless previously 

 stained in toto), and mounted in xylol-balsam. The principal stains used were haenia- 

 toxylin and eosin, or iron ha>matoxylin on the slide; and very good results were 

 also obtained by staining in into with paracarmine followed by counter-staining on 

 the slide with picric acid added to the xylol used in clearing the sections. 



The order of the segments in each horn of a given uterus was preserved as far 

 as possible; the ovarial segment, tube, and ovaiy were put in one series, the next 

 segment numbered 2, etc. In this way much of interest was noted in the variation 



