Folliculina holtoni (S. Kent). 311 



take it. Several of my observations seem at any rate to prove the 

 fact ; for instance, the following : One animalcule which I had met 

 with, quite deprived of an envelope, and which remained a whole 

 week isolated in a drop of water, became rapidly surrounded by a 

 growth of cryptogamic vegetation, bacteria, organic particles of all 

 sorts, etc., which in the vicinity of the posterior part of the body 

 turned eventually to a bluish hue. 



As for the distribution of the coloured matter inside the body 

 there is no general rule, but usually the accumulation is more dense 

 behind, and even more around the nucleus, which then looks a 

 large clear spot surrounded by a dark green frame. 



The nucleus is spherical or ovoid. At first sight it looks a 

 homogeneous pale grey, but under slight compression it is seen to 

 contain numerous spherical nucleoli, which are more intensely- 

 coloured by carmine. Around the nucleus are a few micronuclei, 

 three or four as a rule, which are hardly to be distinguished except 

 in particularly favourable conditions. 



Usually the nucleus is single ; sometimes, however, there are 

 two, united in the shape of an 8 ; more rarely the single nucleus 

 is deeply fissured on one side, as if resulting from a partial fusion 

 of two nuclei into one. 



Thou'Th several observers have indicated a contractile vesicle in 

 the genus Folliculina, it may be considered as certain that the 

 statement has always been due to a confusion with ordinary vacuoles, 

 or with the nucleus itself, which looks a bright roundish spot on 

 the dark surrounding ground. Sahrlage could never find any, and 

 says : " In fact there is none (if as a rule its existence is not to be 

 denied in the marine protozoa)." My own investigations were not 

 more successful ; in Folliculina holtoni there is no true contractile 

 vesicle, and the fact itself is interesting, in reference to the marine 

 origin of the genus ; one must imagine an adaptation to fresh-water 

 without the acquisition as yet of that very characteristic feature of 

 fresh- water animalcules.* 



But if a true contractile vesicle does not exist, there is certainly 

 something that might be considered as taking its place and function. 

 Around the nucleus there are commonly to be seen numerous 

 vacuoles, which appear and disappear at times, and, being quite 

 rounded and sharply delineated, look different from ordinary 

 vacuoles. But more important still are much larger vacuoles, 

 *' lacunar," which grow bigger and bigger, sometimes uniting in 

 large spaces which only the ectoplasmic layer separates from the 

 ■exterior. Sometimes they disappear after having been a very long 

 time growing; and sometimes they enlarge to such proportions 

 that the animalcule itself looks like a bag in which the plasma 



* A contractile vesicle is to be found, however, in numerous marine Ciliata 

 and, perhaps even more, Tentaculifera. 



