116 PROCEEDINGS OF THE ACADEMY OF [PaRT I 



Must we consider Dimorpha as a Heliozoon or as a Flagellate? 

 As a Flagellate, of course, since it is an understood fact that all 

 organisms are to be considered as such, which possess flagella in 

 the adult state; but the affinities with Heliozoa are so great that, 

 in fact, we might look upon this organism as a Heliozoon also. In 

 some of the representatives of this latter group, for instance, Clath- 

 rulina, an embryonic stage is known, where the little being is in 

 possession of flagella; and one might be entitled to ask if Dimorpha 

 could not be a member of the sarcie group, in which the flagella 

 persist up to the adult state? 



In this connection I should like to relate a rather curious coin- 

 cidence: in the same locality there was living, in still much greater 

 abundance, a genuine Heliozoon, of a yet undetermined type, and 

 whose likeness to Dimorpha tetramastix was such that only the 

 possession of the characteristic pearl apparatus and the non- 

 existence of a flagellated state allowed an easy distinction. At the 

 same time, there were occasions when I never could detect any 

 trace of flagella in otherwise typical Dimorphas, and sometimes 

 also the pearl apparatus was hardly to be seen. Dimorpha might 

 be supposed to lose finally its flagella, as well as the pearl apparatus 

 which in some unknown way might be in relation with them? But, 

 leaving that supposition aside, what more beautiful example of 

 mimicry could we imagine? 



Dimorpha monomastix sp. n. Plate V, figs. 7. 8. 



The preceding species was characterized by the presence of four 



flagella; now we find only one. Dimorpha monomastix was found 



in the same locality, and in a much greater abundance, but its small 



size makes it rather more difficult to study. 



The little organism is about 10[jl in diameter, transparent and 

 colorless; in a superficial region are seen dispersed all sorts of gran- 

 ules and food-particles, surrounding an indistinctly delimited clearer 

 central region or endoplasm, which contains the nucleus. This 

 latter is spherical, with a distinct nuclear membrane and a large 

 central caryosome. Very likely this endoplasmic region also con- 

 tains a central granule, which, however, I did not see. There are 

 several contractile vesicles, all very small, except one that might 

 be considered as the principal one, the others being accessory. All 

 around the body are the pseudopodia, of the typical Heliozoan 

 type, but relatively short, measuring about \]/2 times the diameter 

 of the body. The flagellum, always single, is of a moderate length 

 also, about the same as that of the pseudopodia, but strong and 

 thick, much thicker, in fact, than in Dimorpha tetramastix. How- 



