PRESERVATION 



The soft, very delicate and flexible body of planarians can easily be 

 injured and distorted. It is very difficult to preserve its natural 

 shape, particularly the shape of the anterior end or head, which is of 

 some taxonomic importance. Animals killed with alcohol or formalin are 

 often badly contracted and twisted and are difficult to study. The 

 fixing method should preserve the animal well extended. The method 

 recommended by Hyman (1953a: 128) is to place the planarians in a very 

 small amount of water, kill them stretched out with 2% nitric acid 

 followed by 70% alcohol (or any other fixative). De Beauchamp 

 (1932:126) uses a mixture of ethyl alcohol (70%, 7 parts), formalin 

 (2 parts) and glacial acetic acid (1 part) into which the animals are 

 dropped individually; after several hours the fixative is replaced with 

 70% alcohol. Recently Carpenter (1969b) has developed a method of rapid 

 freezing of the extended animals. My favored method is to kill the ex- 

 tended planarians, while they are in gliding motion: in very little water, 

 by pouring over them a hot, almost boiling, fixative, preferably a 

 saturated solution of corrosive sublimate (mercuric oxide, HgCl2) in 

 water or saline, with a subsequent addition of a few drops of diluted 

 acetic acid; after fixing for 4-24 hours the animals are first washed in 

 water, then transferred to increasing strengths of alcohol until a concen- 

 tration of 70% to 80% is reached in which they may remain until further 

 treatment; the last traces of sublimate are removed by adding small 

 amounts of tincture of iodine to the alcohol until the color remains 

 stable. 



None of these methods gives ideal results since there will always be some 

 contraction or distortion of the body or of internal organs. For ana- 

 tomical study, simple shrinkage is better than twisting. 



PREPARATION FOR ANATOMICAL STUDY 



Whole mounts of planarians, stained or unstained, may be prepared by the 

 usual techniques but are of limited value in the analysis of anatomical 

 structures. They will show the number and arrangement of the eyes, the 

 configuration of the digestive system, and possibly some parts of the 

 reproductive system (testes, ovaries, copulatory organs). Details of 

 the anatomy must be studied in microtome sections. 



The specimens are embedded in paraffin or a combination of celloidin and 

 paraffin and serial sections of 5-10 microns thickness are prepared. 

 For the purpose of species identification, sagittal sections are most 

 suitable, transversal and horizontal sections may be useful if sufficient 

 material is available. The choice of histological stains is optional 

 according to the preference of the investigator. A good staining method 

 for the general study and the analysis of muscles and glands is a combi- 

 nation of hematoxylin and eosin. 



