PRACTICAL DIRECTIONS 293 



PRACTICAL DIRECTIONS 



Opallna. Make an incision in the rectum or small intestine 

 of a freshly-killed frog, and mount a little of its contents in water on 

 a slide. Having found an Opalina, note its oval and flattened form, 

 the uniform covering of cilia, the cuticle, cortex, and medulla, and the 

 absence of a mouth and contractile vacuole. Stain with methyl-green 

 or magenta, and make out the numerous miclei. Look out for the 

 products of division, free and encysted. 



MonOCystis. Kill an earthworm by placing it for a few minutes in 

 methylated spirit. Then, with the scissors, slit through the body-wall 

 along the mid-dorsal line through about the anterior third of the animal, 

 when some white, lobed bodies, the sperm-sacs (see Chapter VI) will 

 be apparent. Snip off a very small portion of one of these, place 

 it on a slide in salt-solution and examine with the low power. Amongst 

 the cells of the sperm-sac you will probably be able to distinguish : 



(a) Numerous cysts of Monocystis, many of which will be seen to 

 contain a number of spindle-shaped spores (Fig. 74, E), and in some 

 others, two gametocytes (B). (b} Trophozoites (A) in various stages of 

 growth and contraction. 



Put on a high power, and after observing the groups of cells of the 

 sperm -sacs and sperms in various stages of development, examine 

 in detail : 



1. The trophozoites (A), noting the ciiticle, cortex, medulla, and 

 nucleus. (Observe their movements. ) 



2. The encysted gametocytes, before and after division into 

 gametes (B, c). 



3. Further stages in the formation of gametes and zygotes, and the 

 fully-developed spores (D, E). 



4. The structure of an individual spore, which contains eight sporo- 

 zoites (F). 



5. Sporozoites which have entered a clump of sperm-cells (G) ; and 

 later stages after they have become free, surrounded by the tails of the 

 sperms (H). 



Stain a preparation with magenta or methyl-green, and go over I 5 

 again. 



