Cestoidea 161 



being taken not to injure the caudal vesicle of the worms, and placing 

 them in warm saline solution. Many of the parasites will evert their 

 heads and crawl about actively in the container, using their hooks and 

 suckers as they would when liberated in the intestine. These specimens 

 make ideal whole mounts either with or without staining. 



The behavior of the hexacanth embryo as it leaves its embryophore 

 may be demonstrated by using Hymenolepis nana of rats and mice. 

 Terminal segments of the parasite are chilled in a refrigerator (about 

 20° C.) for a few hours and are then teased apart in a drop of saline 

 on a slide and covered. The slides are gradually warmed to about body 

 temperature and then studied microscopically. This procedure stimulates 

 many of the hexacanths to action and they may be seen jabbing their 

 minute hooklets at the inner membrane of the embryophore. Occa- 

 sionally they entirely free themselves. 



Cysticercoid stages of the smaller cestodes are often difficult to ob- 

 tain. They may be found in naturally infected intermediate hosts in areas 

 of high frequency of the adult parasite in its primary host. Our method 

 of obtaining these stages is to kill a series of rats from various localities 

 to find the highest incidence and greatest intensity of infection with 

 Hymenolepis diminuta. When this is ascertained, beetles (Tenebrio 

 molitor) which serve as the common intermediate host are sought and the 

 adults teased apart in a saline filled Syracuse crystal under a binocular 

 dissecting microscope. The cysticercoids fall away from the surround- 

 ing tissues and may be identified by their inverted heads, broadly oval 

 bodies, and elongate caudal processes. As high as 20% natural infection 

 has been found in this way, with as many as 28 cysticercoids recovered 

 from a single beetle. 



