HYDRAS. 161 



rapidly on the ends of the dice-box, running out to the 

 tips of the tentacles and skirting fearlessly around the 

 edges of the mouth. It is the Trichodma pediculus. 



The Hydra also occasionally has another form of In- 

 fusorial parasite running over its skin. This is some- 

 what kidney-shaped, and has cilia only on one surface of 

 the body. It is called Kerona polyporum. It does not 

 seem so common as Trichodina. 



If the observer desires to preserve the Hydra as a per- 

 manently mounted object for the microscope, he may 

 be easily gratified, thanks to Mr. A. H. Breckenfeld,* 

 of San Francisco, who has devised an admirable method 

 which the writer has tried and recommends. Transfer 

 the Hydras to a slip in a large drop of water, where 

 they can be seen if the slide is held over white paper. 

 When their tentacles are fully extended, " quickly move 

 the lamp directly under the drop, with the top of the 

 chimney about an inch beneath the slide, and hold it in 

 that position for about three to five seconds, the exact 

 time depending principally upon the intensity of the 

 heat. Then quickly remove the slide and place it upon 

 a slab of marble or metal. When cool, pour the drop 

 containing the zoophytes into the prepared cell on the 

 slide which has been held in readiness ; add a drop or 

 two of a suitable preservative fluid, arrange the little 

 animals if necessary by means of a needle or camel's- 

 hair brush (using very great care, however, as the ten- 



* American Monthly Microscopical Journal, March, 1884, p. 49. 



