I 5 2 PROTOZOA 



nuclei that unite, the stationary ones aborting in both mates. 

 During the final processes of conjugation the smaller mate is 

 absorbed into the body of the larger, and so plays the part of 

 male there. But this process, though one of true binary sex, 

 is clearly derived from the peculiar type of equal reciprocal 

 conjugation of the other Infusoria. 



The Ciliata are almost all free-swimming animals with the 

 exception of most of the Peritrichaceae, and of the genera we now 

 cite. Folliculina forms a sessile tube open at either end ; and 

 Schizotricha socialis inhabits the open mouths of a branching 

 gelatinous tubular stem, obviously secreted by the hinder end 

 of the animal, and forking at each fission to receive the produce. 

 A similar habit to the latter characterises Ma/ryna socialis ; all 

 three species are marine, and were described by Gruber. 1 Stentor 

 habitually attaches itself by processes recalling pseudopodia, and 

 often forms a gelatinous sheath. 



The majority of the Oligotrichaceous Tintinnidae inhabit free 

 chitinous tests often beautifully fenestrated, as in Dictyocystis. 



Many genera are parasitic in the alimentary canal of various 

 Metazoa, but none appear to be seriously harmful except 

 Ichthyoplitheirius, which causes an epidemic in fresh-water fish. 

 Quite a peculiar fauna inhabit the paunch of Ruminants. 

 Nyctotherus and Balantidium are occasionally found in the 

 alimentary canal of Man. 2 



The Gymnostomaceae are predaceous, feeding for the most 

 part on smaller Ciliates. We have described the peculiar char- 

 acter of the mouth and pharynx in this group, and the mail-like 

 pellicle of Coleps (Fig. 54). Loxophyllum is remarkable for the 

 absence of cilia from one of the sides of its flattened body, and 

 the tufts of trichocysts studding its dorsal edge at regular 

 intervals. Actinoholus has numerous tentacles, exsertile and 

 retractile, each bearing a terminal tuft of trichocysts, which 

 serve to paralyse such active prey as Halteria. Ileonema has 

 one tentacle overhanging the mouth ; and Mesodinium has four 

 short sucker-like projections around it. 3 It has only two girdles 



1 Zeitschr. wiss. Zooh xxxiii. 1880, p. 439. 



2 Bezzenberger has given a key to the species of these two genera in Arch. Prot. 

 iii. 1903, pp. 149, 157. 



3 We note that Lacrymaria is prolonged in front into a long, slender flexible 

 "neck," with the mouth terminal. This swan-like conformation is "mimicked" 

 by Dileptus and Lionotus, where the neck, like the prostomium of worms, is a mere 



