ii4 PARAMCECIUM, STYLONYCHIA, AND OXYTRICHA 



gametes separate from one another (i), and are found to differ from 

 normal Paramcecium in having each four clear paranuclei. Division of 

 the latter again takes place (K), eight paranuclei being formed (L), and 

 at the same time the nucleus becomes band-like (K, n), and finally 

 breaks up into a number of separate masses (L, M). Next, four of the 

 eight paranuclei unite with one another, forming a single, rounded, 

 granular body (N, p. p), which becomes the permanent paranncleus of 

 the cell: at the same time the remaining four (/. n) increase in size 

 part passu with the gradual disappearance of the nucleus, so that at 

 last a Paramoecium is produced (N, o) having a single normal para- 

 nucleus (p, p) and four large nuclear bodies (/. ), ivhich finally unite 

 to form the permanent nucleus (P). 



Another ciliated infusor common in stagnant water and 

 organic infusions is Stylonychia mytilus, an animalcule vary- 

 ing from y T mm. to \ mm. 



Like Paramcecium it is often to be seen swimming 

 rapidly in the fluid, but unlike it frequently creeps about, 

 almost like a wood-louse or a caterpillar, on the surface 

 of the plants or other solid objects among which it lives. 

 In correspondence with this, instead of being nearly 

 cylindrical, it is flattened on one the ventral side, and 

 is thus irregularly plano-convex in transverse section (Fig. 



23, c). 



It resembles Paramoecium in general structure (compare 

 Fig. 23, A, with Fig. 21, A) ; but owing to the absence of 

 trichocysts the distinction between cortex and medulla is 

 less obvious : moreover, it has two nuclei (, ) and only 

 one contractile vacuole (c. vac}. 



But it is in the character of its cilia that Stylonychia 

 is most markedly distinguished from Paramoecium : these 

 structures, instead of being all alike both in form and size, 

 are modified in a very extraordinary way. 



On the dorsal surface the cilia are represented only by 

 very minute processes of the cortex (c, d. ci.) set in longi- 

 tudinal grooves and exhibiting little movement. It seems 



