114 PROCEEDINGS OF THE ACADEMY OF [PaRT I 



toward a common point. He does not think probable that there 

 could be there a continuous axis which would pierce through the 

 nuclear substance. And yet, according to my observations, the 

 compHcated apparatus of Dimorpha must indeed be thus explained. 

 The axial threads which are seen converging run completely through 

 the chromatic mass, pierce it in fact, and nevertheless they are 

 absolutely continuous and homogeneous." 



These observations are interesting, in so far as they show the 

 flagella to be inserted quite near the central granule; but both 

 Blochmann and Schouteden are certainly wrong when they consider 

 as a nucleus that particular apparatus which we have seen in Di- 

 morpha tetramastix consists in radiating lines of pearls. In reality, 

 the true nucleus, generally concealed by the accumulation of gran- 

 ules and food -particles, easily comes to view by means of a slight 

 compression of the animal. It quite conforms in character to an 

 ordinary Heliozoan nucleus, being rather large, homogeneous, vari- 

 able in its shape, and always somewhat excentric in position.^ There 

 are several contractile vesicles, variable in number, but so obscured 

 by the mass of granules and food-particles that fill the external 

 layers of the body, that one hardly sees them. 



Such is the Heliozoan form of Dimorpha tetramastix; but if we 

 keep the animalcule under observation for a while, after five, ten, 

 twenty minutes or more, we can see its transformation into the 

 flagellate state. Suddenly, and without any apparent motive, the 

 pseudopodia are seen to retract, at the same time as the body length- 

 ens, and the central granule with the surrounding chaplets of pearls 

 moves forward; and after a single second of time, or at most two, 

 the Heliozoan has disappeared, and instead we have a true Fla- 

 gellate (Plate V, fig. 5), more or less lengthene, with an anterior 

 depression from which arise the two pairs of flagella. Something, 

 however, is frequently left of the pseudopodia, in the form of lateral 

 or, more often, posterior appendages, more or less covered with 

 granules (Plate V, fig. 6); and some of the axial threads are still 

 visible, trailing inside the body, behind the central granule 

 which is now quite near the anterior extremity. 



It is possible only under particularly favorable conditions to 

 get a clear view of the phenomenon of the mechanism of that sud- 

 den transformation, but I was able to observe it several times and 



2 Blochmann, in his figure of D. ynutans in the Heliozoan state, has in fact 

 xepresented the nucleus, but as a "particle of food." 



