174 BIOLOGY 



with fine scissors, an incision is made along the dorsal median line, from 

 the head to the posterior end of the body. The body is then opened and 

 the walls pinned out so as to disclose the internal parts. This should all 

 be done under water. If carefully performed the internal parts may be 

 easily worked out, a lens being used to show the smaller parts. To show 

 the nervous system and the nephridia the alimentary canal should be 

 cut through, behind the gizzard, and carefully dissected away in front. 

 There will then be no difficulty in making out all the organs except the 

 ovaries and spermaries. The ovaries may be found by careful study 

 with a lens, but the spermaries cannot be found without special methods. 

 The contents of the seminal vesicles and the ovaries should be examined 

 with a microscope. One of the nephridia should be removed and studied 

 with a low magnifying power. 



For the study of the histology, sections should be furnished by the in- 

 structor. Animals preserved as above described are in good condition 

 for sectioning. They should be embedded in paraffin and stained in picro- 

 carmine. Sections through various parts of the body should be studied, 

 and these should include at least sections through the cerebral ganglia, 

 through the aortic arches, and through the posterior parts of the body show- 

 ing the typhlosole. The study of these sections with both low and high 

 powers will show the chief features of the microscopic anatomy. More 

 detailed study of the histology is hardly feasible with elementary classes. 



