INVERTEBRATE ZOOLOGY. 125 



ventral chaiu. supplying the mouth-parts. From this a nerve cord passes 

 through the neck and unites with the first thoracic ganglion. 



98. Study of the minute structure of the partH (Histology). This is done 

 mainly by means of very thin sections artificialh' stained and cut by the 

 microtome. The sections are to be prepared by the instructor, mainly in ac- 

 cordance ■tt'ith rules given in this book, to be learned later by the students, 

 and distributed during the laboratory periods. The students are to bring to 

 the microtome a clean microscopic slide (object-glass), the center of which 

 has been smeared with a thin layer of Schiillibaum's collodion fixative. The 

 section, together with the paraflfine, is placed upon this, heated gently by 

 pas.sing it through the top of a Bunsen gas-flame two or three times (a hot 

 radiator is often sufficient) until the paraffine is melted. The slide is then 

 immersed in a jar of turpentine (a few drops of turpentine may be poured 

 over the slide instead) imtil the i)araffine and excess of fixative are entirely 

 removed. The slide is then to be carefully wiped with a clean cloth, leaving 

 a small area about the section, a drop of Canada Balsam x)laced upon the sec- 

 tion and a cover-glass gently laid on. Imprisoned air-bubbles vriW work out 

 of the preparation in a short time. If correctlj* done, each portion of the sec- 

 tion should be in the same position as when in the paraffine. If a portion 

 floats off in the turpentine, the slide was not heated enough, or perhaps not 

 enough fixative was used. Too thick Balsam will often push the section 

 apart. Sections and other preparations may be made ad libitum of anj' por- 

 tion but the following preparations are recommended. They are best used to 

 accompany the dissection, but as fresh specimens are necessarj' for dissection, 

 while carefully preserved material is sufficient for sectioning, it is often expe- 

 dient to finisli the dissection during the season in which living grasshopijers 

 are readily obtainable. 



1. Digestive system. 



(a) Cross-section of crop in region of teeth. 



(b) A piece of the wall moiinted flat, to compare with the last. This 

 may be done by the stiident. as follows : Place in three watch- 

 crystals, 95^^, 100^, and oil of cloves (or turpentine). Select the piece 

 desired and place it 5-10 minutes in each of the fluids and in the 

 order given. In this waj' the water is entirely extracted and the 

 specimen prepared for reception into the Balsam. For this, place a 

 drop of Balsam in the middle of a slide, and spread out the speci- 

 men in it. inner side uppermost. It is then to be covered in the 

 usual way. 



