and Laboratory Methods. 2361 



In collecting specimens of Plaiiaria one can get the best results by wading 

 into the stream and picking up the stones from the bottom and examining their 

 under surfaces. Where the collecting is good twenty or more specimens of 

 Plaiiaria may be found on the under surface of a single stone not over three 

 inches in diameter. The specimens may be most expeditiously removed from 

 the stones by gently slipping a thin spatula or section lifter under their bodies 

 and lifting them ofT in this way. The specimens may then be shaken off the 

 section lifter into a bottle of clean water for transportation to the laboratory. 



Rhabdocoeles may be obtained in numbers by taking a quantity of plant 

 material from a stagnant pool and then putting this into culture dishes with 

 clean water in the laboratory. The rhabdocoeles will soon appear at the surface 

 of the culture and may be taken off with a pipette. Rhabdocoeles may also be 

 collected with a Birge net in places where they are abundant, 



All planarians live very well in aquaria in the laboratory. The only precau- 

 tion necessary is to see that there is not too much decaying vegetable or animal 

 material in the aquarium dish. Planarians will eat voraciously the crushed 

 bodies of fresh water moUusks, as for example, Physa or Linvuea. The ease 

 with which planarians may be kept alive in the laboratory makes them very use- 

 ful objects for the teacher. 



The best killing and fixing fluid for planarians, in case one wishes to pre- 

 serve them, is corrosive acetic. 



Formula : 



Saturated aqueous solution of corrosive sublimate 95 parts. 

 Glacial acetic acid ------ 5 " 



Fix for one-half hour ; wash in TO per cent, alcohol-tincture of iodine. Avoid 

 touching the fluid or objects with metal. 



After fixation in this fluid the specimens should be preserved in 70 per cent, 

 alcohol. 



It is apparently impossible to kill planarians in a fully extended condition, 

 and in general preserved specimens are much less satisfactory than living. 

 Since planarians may be collected and kept alive in the laboratory so easily there 

 is very little reason for preserving them unless one wishes to study their histo- 

 logical structure. 



They may be shipped alive for purposes of identification if they are placed 

 in a vial of perfectly clean, filtered tap-water, without any other material, either 

 animal or vegetable. No air space should be left at the top of the vial between 

 water and cork. Such vials may be shipped by mail in any of the regular mail- 

 ing cases adapted to the transportation of fluids. 



(3) Uses to ivhich Planarians may be put by the Teacher. 



A. To demonstrate the process of regeneration. 



Planarians have a very marked capacity for reproducing or regenerating 

 parts of the body lost through accident, or as the result of operative procedure. 

 If the head of a planarian be cut off a new head will be formed in a compara- 

 tively short time. This is an extremely significant physiological phenomenon 

 and one which cannot fail to arouse the interest of students. The experiments 



