308 AQUATIC PHYCOMYCETES 



rhizoidal system not observed; zoospores about 1 u, in diameter, prob- 

 ably escaping through a minute pore. 



On heterocyst of Calothrix sp. (marine), Sweden. 



On Aquatic Phycomycetes 



? Rhizophydium parasitans Scherffel 

 Arch. Protistenk., 53: 26, pi. 2, figs. 52-56. 1925 



Sporangium sessile, spherical, 8-10 u. in diameter, with a thin smooth 

 colorless wall; endobiotic part not observed; zoospores spherical, 

 mostly 4 \x in diameter, with a colorless eccentric globule and a posterior 

 flagellum about 24 u. in length, emerging through a wide pore at the 

 apex of the sporangium and either forming a compact motionless 

 group at the orifice before dispersing or escaping individually and amoe- 

 boidly, in either case assuming suddenly a lively hopping movement; 

 resting spore sessile, spherical, 6 \x in diameter, with a thick smooth 

 colorless wall, the outer margin dark and sharply defined, contents 

 coarsely granular, with an eccentric colorless fat globule, 2 \i in diam- 

 eter, germination not observed. 



Parasitic on sporangia of Rhizophydium goniosporum parasitizing 

 Trihonema bombycina, Hungary. 



A curious condition of hyperparasitism is shown by this species. 

 Scherffel noted that certain sporangia of Rhizophydium goniosporum 

 had within them a spherical thick-walled resting structure or "cyst" 

 of uncertain origin. The sporangia of R. parasitans were found only 

 on sporangia of R. goniosporum which contained the remains of these 

 cysts. Against the hypothesis proposed by Scherffel, namely, that the 

 epibiotic sporangia of R. parasitans were in reality sporangia formed 

 by germination of the endogenous cysts, was the fact that epibiotic 

 resting spores also occurred on R. goniosporum. These were never 

 found, however, on sporangia bearing the endogenous parasite. If 

 these facts present the correct interpretation of the structures observed 

 by Scherffel, then the sporangial stage of the species is parasitic on the 

 encysted stage of an unidentified organism, possibly a monad, which 

 in turn has parasitized the sporangium of R. goniosporum, which in 

 turn has parasitized the alga Trihonema! The resting stage of R. para- 



