FIFTEENTH WEEK. 



The work of this week is elective. For directions see under 



twelfth week. 



ELECTIVE WORK. Morphology (con.) 



THIRTEENTH WEEK. The tongues stained last week are removed 

 to fresh strong alcohol a few minutes, then to oil of cloves about two 

 minutes, until they have become uniformly somewhat clear. They are 

 now put into barely melted soft paraffin (50 C.) for one-half hour, then 

 for one hour into harder (55 C.) Ladle out onto a wet cold plate of 

 glass, so as to form thick drops with a tongue in the middle of each. 

 After they are thoroughly cool trim into rectangular blocks and fasten 

 one by means of a hot knife blade to the object holder of the microtome 

 in such a position as to cut cross sections. Cut as thin as possible, ad- 

 justing the temperature of the room to the hardness and thickness of the 

 section, so that, while the sections will not wrinkle, they will stick to- 

 gether and form a perfect ribbon. Keep the order of every section 

 very carefully should the ribbon break. Mount as follows: Paint a thin 

 layer of Schallibaum's fixative on a slide. Arrange the sections in the 

 order cut, using two slides if one is not enough. Place in the oven of 

 the bath at 55 C. five minutes. Wash while hot with turpentine and 

 apply the balsam and cover at once. 



FOURTEENTH WEEK. Cut and mount two more sets of section 

 longitudinally and at right angles to each other. 



FIFTEENTH WEEK. Draw carefully the whole tongue from two 

 directions. 



SIXTEENTH WEEK. Draw the two most comprehensive longi- 

 tudinal sections and a number of cross sections and indicate on the 

 other drawings the approximate place of these. 



GROUP III Developmentoftheplantlou.se. Needed: Salt so- 

 lution, alcohol, oil of cloves, balsam, glycerine jelly, a watch glass, 

 needles in handles, slides, covers, microscope, a number of plant lice. 



TWELFTH WEEK. Dissect in salt solution a full-grown plant louse, 

 isolating the ovaries. Mount in glycerine jelly as directed under field 

 work and examine under the microscope to see if the embryos are whole 

 and sufficiently separated from each other and from the other tissue. 

 Mount a good number of slides. 



THIRTEENTH WEEK. Dissect as above and mount in balsam a 

 number of slides. 



FOURTEENTH WEEK. Study the slides and pick out a series of 

 about six stages in jelly and in balsam, showing the development of 

 the young louse. Compare Mark. Die Pflanzenlause. 



FIFTEENTH WEEK. Draw the three smaller stages, naming all 

 the parts which can be recognized. 



SIXTEENTH WEEK. Draw the older stages as above. 



